"I have a netbook with an Atom processor"
The "Low System Requirements" category is reserved for games that will run on just about anything you put them on. This is a category meant for literal toasters like the aforementioned Toshiba NB505 (systems meant exclusively for work) that can only put out so much in terms of game performance. Note that these games will run on anything, so if your toaster is able to run anything in "Medium" or "High" requirements, these should be a cinch to install and have fun with as well.
The classic and quintesential Medevial RTS. Enough content to keep a single player entertained paired with limitless multiplayer fun makes AoE2 a go-to toaster game. The Genie Engine provides a lot of computer system flexibility, not requiring a whole lot of horsepower in the modern age.
Age of Empires 2 as it was on release is kind of hard to acquire legally, but it can still be done somewhat. This listing on Amazon is available as of January 25th, 2016. Otherwise, I suggest pirating an old copy of Age of Empires 2. If you want to be safe legally, the HD edition is available on Steam, although it does not have the same performance as the original.
One hell of a demonic ride, this game requires a bit more oomph from your toaster than DOOM but not a whole lot more. Stab cultists, burn monsters, and blow up zombies all in the name of glorious revenge. Planned modernization in the form of the DarkXL engine.
Blood, One Unit Whole can can be purchaesed on Good old Games.
A cult classic freeware RPG filled with self-aware humor that exploded in popularity in recent years. Built with Gamemaker, it ran on just about anything I put it on. A sequel for Barkley Shut up and Jam Gaiden is currently in development.
Barkley Shut Up and Jam! Gaiden is available for download at Tales of Games's website.
One of the flagship roguelikes alongside Nethack and the original Rogue, Dungeon Crawl Stone Soup comes with all of the lightweight high performance gameplay from almost all of the games in the subgenre. Accept no substitutes! Dungeon Crawl: Stone Soup can be played locally or online in a web browser.
Dungeon Crawl: Stone Soup is supported on a very large variety of operating systems. For ease of access, the downloads for DCSS can be found on the DCSS Download page. DC:SS also comes preloaded onto certain Linux distros such as Ubuntu, Debian & other derivatives. If it is not preloaded onto your Debian-like distro, you can open up your terminal and type
sudo apt-get install crawl-tiles
A bit less ancient than DOOM but it hasn't stopped anything I've put it on just yet. Modernization for Descent 1 and 2 is available with DXX-Rebirth, which improves visual aspects, the HUD, ability to play on Linux/*NIX systems, and even allows for custom music.
Named by many both on and off the record to be one of the single greatest PC games ever made, Deus Ex has stood the test of time in terms of both gameplay and performance. In our case, Deus Ex doesn't ask for much when it comes to modern computers.
The predacessor to the famous ARPG, Diablo 1 is prime mob grinding without any of the performance requirements. Worked out of the box on the NB505, but for modern Windows Operating Systems you'll need to make a .bat file to bypass a compatability error that results in odd on-screen colors. You can find the contents of that file here.
Diablo can be purchased on Amazon, but since the game is no longer distributed by Blizzard, you might be better off trying to find a copy on a torrent tracker of some kind.
The immortal, all-powerful, and genre defining game: DOOM. One of the best damn games ever made, it spawned a number of equally fun and destructive games like Chex Quest, Hexen, and Heretic. DOOM has thousands of hours of replayability with a litany of .wad files (custom levels). Runs on quite literally anything these days, even printers and calculators.
However, you will still need a legal copy of DOOM (or the right .pak files) to utilize these modern ports. DOOM is available for purchase on:
It's DOOM with a rougelike twist! What's not to love? How you rip n' tear is completely up to you, down to the visual style of your game: slick looking tiles or familiar ASCII. Comes with all the adventure and technical performance of a roguelike in the familiar world of DOOM.
DOOMRL was made by Kornel Kisielewicz and Derek Yu, and can be downloaded from the DOOMRL Homepage.
The man, the myth, the legend: Duke Nukem, all-American badass. This is Duke's first FPS appearance and is neck and neck with DOOM as a ferocious shooter with attitude. Duke Nukem 3D hasn't been shown to run on printers or calculators but we're probably already there at this point.
However, you will still need a legal copy of Duke Nukem 3D (or the right .GRP and .RTS files) to utilize EDuke32.
The game that started it all for Valve Software, cultivating a very large and loyal fanbase. Half Life 1 ran surprisingly well on my netbook as the original minimum requirements only ask for a processor that can put out 500mhz, but Half Life: Source needs a processor that can put out 1.2ghz and at least 512mb. Somewhere along the line they changed the MP5 to an M16 as well as the sound it makes when it fires in the Steam version. I hate change.
Lovely Planet is far from your average shooter. Relying more on speedrunning memorization and reflexes rather than combat as gameplay, Lovely Planet is a fun and welcome change from the norm. Built on the Unity engine, the game is a whopping 83 megabyte install. Holding 60fps was laughably easy on my netbook. Be advised that the game is particularly repetitive but I believe that the level variety makes up for that fact.
The daddy of WWII FPS games, covering most of the major battles in the European theater of war. Even though it's easy to adapt to modern control schemes, it'll feel a bit dated to those not well-versed in FPS games. MoH:AA is built on idTech, which is particularly friendly to low-end machines since 2007 or so. FPS was steady in the high 60s on the NB505.
The Medal of Honor Allied Assault War Chest is available on Good old Games.
Quake is one of the legends that set an unnatural amount of standards for FPS gameplay. Steam users will want to install the fan-made "Ultimate Quake Patch", which is a graphical installation of the DarkPlaces engine which brings a decent amount of modernization to Quake. Some fans of Q1 find fault with Quake 2 but Quake 2 is also worth your time on a toaster. Quake 3 is worth it if you have others friends on toasters to play with.
Quake, like DOOM, can be acquired on both Steam and Good old Games:
Keep in mind that you will still need the necessary .pak files to play the full game on your Linux system. Visit the Quakespasm homepage for more information.
sudo apt-get install quakespasm
There is but one Lo Wang and he exists in Shadow Warrior Classic. Made by 3DRealms with a protagonist who was easily as badass and comedic as Duke Nukem, anyone playing Shadow Warrior Classic(/Redux) will have no trouble finding a machine to run this game.
Shogo Mobile Armored Division is a love letter from America to Japan written by Monolith Productions (known for the F.E.A.R series among others) in 1999. An interesting take on FPS games, players will find themselves shifting between fighting on foot and fighting in mechs (while control-wise, there is no difference) and going through a generic but enjoyable wartime story. Shogo: MAD ran flawlessly on my netbook, 60 FPS was a minimum.
Shogo: Mobile Armored Divison can be purcahsed on Good old Games.
Take the role of Kyle Katarn and stop the Dark Troopers, exploring a lot of unique Star Wars locale. The original is made in a proprietary Lucasarts engine called the Jedi Engine that is very similar Build Engine, so if you have played DOOM/ChocolateDOOM before, the experience will be familiar. Grab DarkXL to solve modern compatability issues and add a modern control scheme with mouse support. Dark Forces vanilla ran flawlessly on my NB505.
Made on the Genie engine like AoE2 complete with all of the global compatability and performance that comes with it. Surprisingly active modding scene. The various campaigns are pretty "same-y" where you are either given a limited number of units to command or a base to build up, but is still highly enjoyable regardless.
Star Wars Galactic Battlegrounds can be purchased on Good old Games.
If AoE2 is the defining Medevial RTS, Stronghold is the defining Castle Management Strategy game. Storm some king's castle, defend your own, or just watch your stockpiles grow and manage a comfy keep; Stronghold does all this while running on just about anything.
Another member of the "gameplay & storytelling balance" club, System Shock 2 offers a sci-fi experience like no other game. Recently recieved a revamp (distributed on Steam and Good old Games) that allows for gameplay across Windows, OSX, and Linux (although the latter is apparently simply an instance of WINE). A very system friendly game.
An old hand of the roguelike family, Tales of Maj'Eyal has enjoyed a recent bout of success following its launch on Steam. Ran into a few hiccups playing ToME on my netbook, but ran pretty well regardless. Will run flawlessly on modern low-power systems across all three major operating systems (Windows, OSX, Linux).
Tales of Maj'Eyal can be purchaesed on Steam or Good old Games. Purchasing Tales of Maj'Eyal supports the developer (although GoG and Steam get a cut), but the game can be downloaded for free at the Tales of Maj'Eyal homepage.
A series that started on the PSP, Legend of Heroes: Trails in the Sky has made its way to the PC. XSEED did an amazing job porting TitS and it has run on everything I've put the game on. The Second Chapter is also available on Steam and Good old Games, and hopefully the Third Chapter will make it here as well.
If you can't stand the English battle voice-overs (fear not, there's no spoken dialogue outside of combat), a simple google search reveals a Japanese Voice Over Patch that can be applied. An explanation for the lack of Dual Audio is provided here.
Warcraft 3 has been stuck in the mind of an entire generation for a myriad of reasons: competition in the base game, DotA, the various user-created minigames, and so on. Even with most of the multiplayer aspects devoid of human life, the Warcraft 3 campaign is worth experiencing and can run on just about anything.
Nihon Falcom has pumped out many memorable series over the years, and Ys has yet to dissapoint. XSEED has done a wonderful job porting over 5 Ys games for Western consumption, and the system requirements for all 5 of the currently available games are particularly low. I haven't tried Oath in Felghana, Ark of Napishtim, or Origin on my netbook but after seeing Trails in the Sky work on my netbook, I would recommend giving the games a shot no matter what your computer's specifications are.
All of the Ys games can can be purchaesed on Steam or Good old Games.