Looking for a bit of PC gaming nostalgia? You could dig those old floppy disks out of your closet...or you could grab the new, improved, open source versions of those games online for free.

"Source ports" are older games like DOOM and SimCity that have been released as full open source code by their creators, then updated and improved by the community. The re-released games are passion projects, and almost always free to download on the PC. They typically include improved graphics, bug fixes, and new features, sometimes even entirely new weapons or game modes---perfect for a nostalgia trip that still feels fresh. They're definitely worth a try if your Steam library is looking a bit dusty.

Brutal Doom

Brutal Doom is kind of, well, brutal. This video is a probably NOT SAFE FOR WORK.

The classics of the first person shooter genre have all been made and remade in open source flavor. Duke Nukem, Quake, and Wolfenstein are all well-represented on freeware databases, and of course the original DOOM has hundreds of variations on just about every platform ever released. For my (lack of) money, the best of the bunch is Brutal Doom, a bigger, louder, bloodier version of the original from modder Marcos Abenante.

Brutal Doom is best known for its over-the-top blood, gore, and eviscerating animations (and it's not as if the original DOOM was family friendly). But there are a ton of gameplay improvements, too, incorporating some modern design into the classic shooter. Teams of marines will help you shoot Hell's legions of demons, you can use vehicles and sneak up for stealth kills, and tons of new weapons and bad guys keeps the old game fresh. Give it a try if you're a fan of the original, or the recent (also great) reboot/sequel/whatever who wants to see what the hubbub was about back in 1993.

FreeSpace 2 Source Code Project

FreeSpace 2 is considered one of the best entries in the space combat genre, breaking the somewhat stale mold that had been set by entries like Wing Commander. In addition to an impressive variety of ships and a solid single-player campaign, players could go head-to-head in a consistent online universe that shifted as the various factions fought. Unfortunately, it came out in 1999, just as space combat was taking a dive in the PC gaming market, and the developer released the full source code just three years later.

Enter the FreeSpace 2 Source Code Project. For fifteen years (yeah, really!), independent developers have been tweaking the original game to perfection, adding improved graphics and effects, expanding the campaign, and keeping the innovative multiplayer systems alive. You can still buy and install the original, commercial version of the game, but why would you?

WinROTT (Rise of the Triad)

In 1994, Rise of the Triad was something of an experiment. While the first-person shooter boom was still in full swing (in fact, the game started as a Wolfenstein sequel), this action game mixed things up with multiple playable characters with distinct attributes, a focus on exploration and logic, and some of the first expansions of real-time enemy AI. The gangster bad guys can steal your weapon, lure you into traps, or spring ambushes. Oh, and Rise of the Triad marks the introduction of "gib" gore physics, something that thrilled gamers and terrified senators for years to come.

After the developer released the code in 2002, a couple of fans got to work on a proper Windows port, since the original had been released on DOS. There are plenty of other ports, but "WinROTT" is probably the most complete, since it fixes many of the original game's bugs, adds higher-resolution textures, and preserves the multiplayer modes. Oh, and the dog mode is still there, too---eat your heart out, Call of Duty.

Commander Genius

Id Software is mainly known for Doom, Quake, and Wolfenstein, but back in the day, the developers had less groundbreaking projects that were also well-loved. Commander Keen brought some of the goodness of Mario and Alex Kidd (this was before Sonic, kiddos!) to PC players in the form of a colorful side-scroller with smooth, fast-paced graphics. A handful of PC sequels followed, including the same kid-friendly stories (and a lot of unlicensed Pepsi imagery).

The Commander Genius project updates the original games with an emulation layer, allowing them to be played, improved, and customized on more or less all modern desktop systems. The project hosts the original shareware episode for free, and if you can track down the files for the other games, you can apply the same improvements. If you can't find your floppy disks, the original trilogy and Keen Dreams are now available on Steam and other digital storefronts---Commander Genius should work with them, too.

OpenJK (Star Wars: Jedi Knight series)

If EA's abuse of the Star Wars license has you down, why not relive some of the most-loved single-player Star Wars games ever? The Jedi Knight games, released between 1997 and 2003, feature standard shooter gameplay as well as third-person lightsaber combat, the latter of which is still beloved as some of the best of any Star Wars titles. Add in competent story campaigns and a frantic multiplayer mode, and you have a recipe for greatness.

The original games are somewhat dated now, but developer Raven Software released the source code for Jedi Knight II: Jedi Outcast and Jedi Academy following the closing of LucasArts. A team of dedicated fans have kept these two latter entries updated and improved via the OpenJK project. Ports are available on macOS and Linux, and the team is working on Jedi Outcast as well.

Micropolis (SimCity)

Thanks to the One Laptop Per Child project, the source code for the original SimCity was released in 2008 so the game could be included in the hardware. An open source port of the original city builder followed, calling itself Micropolis (the original development title for Will Wright's famous game way back in 1989). The code has been widely distributed since then on multiple platforms---you can even play a version in your desktop browser, no download required. It's a great way to experience the original game that inspired decades of management simulators.

D2X-XL (Descent series)

Descent and Descent 2 are still talked about by space shooter fans thanks to their innovative, motion-sickness-inducing six-axis control scheme for moving your ship around in zero gravity. In fact, it's often considered a first-person shooter at heart, since the movement system is so different from the flight sim-style controls of other space games. The source code fro the original two games was released in the late 90s.

Since then, several open source Descent projects have sprung up, but the most ambitious is D2X-XL. In addition to updating the originals to run on modern PCs with higher resolution textures, new visual effects, a more helpful interface, and even brand new mission campaigns, the open source update adds support for the Oculus Rift headset. So now it's a real first-person shooter.

Project Magma (Myth series)

Before Bungie decided to evolve combat with Halo and then evolve DLC blunders with Destiny, they made a real-time combat series (that, um, wasn't Halo Wars). The Myth series was one of the first to combine real-time strategy and 3D graphics, offering flexibility for the interface and combat tactics. While not one of the huge strategy games of its time, it was well-loved by fans, and online multiplayer remained popular for years.

Project Magma is a group of fans and developers dedicated to preserving the original Myth: The Fallen Lords, Myth 2: Soulblighter, and Myth III: The Wolf Age. The second game has also been given special attention for huge improvements, including high-res texture packs, new game modes, and map-making tools. There are also more than a dozen map and campaign packs for new stuff, including expansions on the original mod and total conversion to turn the online multiplayer into a paintball war or the American Civil War.

OpenTyrian

Tyrian isn't one of the great side-scrolling shoot-em-ups, but it's a staple of shareware compilations: a competent and colorful throwback to classic arcade games like 1942 and Gradius. The original was released as shareware, with the first level being free and the rest of the game selling commercially. In 2007, the source code and some of the licensed artwork was released to private developers, who've maintained ports for PC and mobile systems ever since. It's a great choice if you're looking for some retro "bullet hell" gameplay.

Image credit: scp.indiegames.us, CloneKeenPlus.sourceforge.net, micropolis.mostka.com, Descent2.de