Mods for games are almost essential to the video game ecosystem. They keep interesting older games alive much longer than they would otherwise, offer players more options in how they play, and encourage would-be game makers to become modders or even developers themselves. While some mods fix broken mechanics or add quality-of-life features, others add new quests and storylines, and some mods even alter the genre of the game itself.

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However, some mod projects are so ambitious that the end result may as well be its own standalone title. And many of them are. Players with access to certain games (i.e., they already own them) may be delighted to discover that their purchase actually got them a freebie just as good as the game they had set out to buy. The following are examples of games that explicitly used the engine or assets of the original and became their own (free-to-play) titles.

6 Nehrim: At Fate's Edge

TES: Oblivion

For any Elder Scrolls fans currently looking longing back at Oblivion, wishing they could hit up a new game but experience it all afresh (without the encyclopedic knowledge of the Heartlands and its lore still somehow embossed into their brains), there's Nehrim: At Fate's Edge. Rather than taking place in Tamriel or the Elder Scrolls universe at all, Nehrim offers a diverse world, a new story, and heaps of original lore to dig into.

While being of the same size as the Elder Scrolls 4, Nehrim's world arguably rivals the fine work of Bethesda's artists as each part was hand-crafted by the modders, giving each place a more distinct feel. The mod also fixes, among other things, what was to many one of the most egregious aspects of Oblivion, the leveling system, instead taking cues from Gothic's point-buy system.

5 Chronicles of Myrtana: Archolos

Gothic 2

Some very talented fans of the original series Gothic series put together what can scarcely be called a simple "mod" by the name of Chronicles of Myrtana. It's basically an expansion on Gothic 2 that gives players access to Archolos, a place mentioned multiple times in the lore but never explored in the games.

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For many older gamers, the Gothic series is an easy shortcut to get to Nostalgia Avenue, and Chronicles of Myrtana doesn't just imitate the beloved eponymous setting and classic RPG feel but absolutely nails them both. Lateral thinking is rewarded during quests. The world is open-ended and feels like it works independently of the player. Additionally, the voice acting was performed by pros, which helps maintain that all-important immersion.

4 DOTA

Warcraft 3

DOTA (Defense of the Ancients) began life as a Warcraft 3 mod (inspired by a StarCraft game mode called "Aeon of Strife," in which players took control of a single unit rather than groups), taking the community by storm upon release. Valve, known for building on existing games (Team Fortress has its roots in Quake, and their famous Source engine was heavily based on Quake's engine), took immediate notice of the crowd draw Kyle Sommer, the mod creator, was pulling with his mod.

DOTA rewarded players with high levels of skill and a working knowledge of its deeply refined systems and basically created a whole game genre overnight. It is still available to play today, although its player base is obviously much smaller than that in the sequel game.

3 S.T.A.L.K.E.R.: Anomaly

Call of Pripyat

The only problem with the S.T.A.L.K.E.R. games (besides having to type the period after each letter on a keyboard) is that it never feels like there's never enough S.T.A.L.K.E.R. to go around. Thankfully, some passionate modders out there feel the same way. While a few total conversion standalone mods for the games exist, Anomaly is one of the standout overhauls. Four chapters of a whole new original story and a sandbox more are more than enough to keep fans engaged.

There's also a warfare mode that sees the various factions of the Zone fight for supremacy in real-time across the mop. As a word of warning, Anomaly is for those who like to play on Stalker's "misery" difficulty, so basically, those who thrive off of brutal, hardcore challenges in their FPS experiences. One cool feature is the in-game PDA, which will help players navigate the map with complete immersion.

2 Crossfire

Freelancer

For a game that is 20+ years old, Freelancer sure has a dedicated fan base. Take Crossfire, essentially a fan-made sequel (or, more accurately, sequel / DLC) to the original open-ended system-hopper from 2003, which was released in late 2015. The Crossfire campaign can be started without playing the vanilla game, but with the tougher combatants and vast distances between over 160 new planets and stations, it might be good to get a few ship upgrades first.

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The mod team behind Crossfire painstakingly created gorgeous music, ships, and (destructible!) environments for players to explore, not only reminiscent of the base game but a perfect complement to it. As a plus (or perhaps a downside), while even the most die-hard Freelancer fans might have complained about Freelancer's overly easy dogfights, Crossfire provides exceptionally challenging ship-to-ship fights, with fights being a slugfest for the ill-prepared.

1 Enderal Special Edition

TES: Skyrim: Special Edition

Enderal: The Shards of Order (and more recently with the expansion, Forgotten Stories) completely converts the snow-dusted landscape of Skyrim into a tropical open-world masterwork, complete with its own stories, difficulty scales, mechanics, music, and much, much more. There are plenty of examples of games built in Skyrim that should become their own game (one outstanding mod, The Forgotten City, did eventually become its own game), but none come close to this mod.

Anyone with a copy of Skyrim (both Legendary and Special Edition) can download and play Enderal for free and experience the moody and compelling world filled with top-notch voice acting, hand-crafted environments (ruins, jungles, towns), and mad lore that could give even The Elder Scrolls writers a run for their septims.

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