Free TTRPGs

Want to play a TTRPG for free? Here are some recommendations. 

Basic Fantasy RPG is a retroclone of a 1978 version of D&D Basic, the rules-lite version of Advanced D&D. Basic Fantasy differs because it has ascending armor class rather than a to-hit matrix. It has free supplements including adventures compatible with any game based on versions on pre-3e D&D. https://www.basicfantasy.org/srd/

OSRIC stands for Old School Reference and Index Compendium, and is a retroclone of Advanced D&D from 1978, which is the crunchier version of D&D Basic. https://www.leveldrain.com/srd

Alternative to OSRIC, the creator of Basic Fantasy RPG also made another retroclone of Advanced D&D called Iron Falcon. Or is it a retroclone of Original D&D?  https://www.drivethrurpg.com/en/product/148344/iron-falcon-rules-for-classic-fantasy-role-playing

Olde Swords Reign is a combination of 0e D&D and 5e D&D. The author of Olde Swords Reign says his game is compatible with Basic Fantasy RPG, and it is. I would recommend using the character creation rules from Old Swords Reign when you play Basic Fantasy RPG to mix the old and new. https://osreign.com/

The Black Hack is based on D&D Basic, but with a lot of changes to make it even more rules-lite than Basic Fantasy RPG. https://the-black-hack.jehaisleprintemps.net/english/

Cairn (or Cairn RPG?) is a new game inspired by a few other New School RPGs like Into the Odd and Knave. If you're absolutely new to RPGs, I recommend you start here. It is very rules lite, emphasizing narrative over mechanics. These rules can be setting and genre neutral, but Cairn Second Edition comes with a very fleshed out setting. https://cairnrpg.com/

Cairn's website hosts a few "hacks" of the Cairn ruleset that changes them to suit specific types of games, such as Liminal Horror RPG which does horror. https://cairnrpg.com/hacks/third-party/even-more-third-party-hacks/

Index Card RPG (ICRPG) has a free quickstart ruleset available for download on this website Drivethrurpg.com. This is a game is basically a collection of house rules for D&D 5e that became its own system and distinct from 5e. It is rules lite, and is setting and genre neutral. Very, very easy to learn and understand. Very fast and easy to play. https://www.drivethrurpg.com/en/product/221038/index-card-rpg-free-quickstart

Open Legend RPG is a setting and genre neutral RPG. Rather than give you a catalog of classes, races, powers, etc., it gives you a catalog of pieces that you can use to make your own. Character creation is a bit more complicated and involved, but it resembles what D&D fifth edition could have been if the developers had more creative freedom. https://openlegendrpg.com/

Cogent Roleplay is a dice pool style of game. That means your stats tell you how many six-sided dice to roll for actions, and then you count the number of dice that are successes. What stands out to me most is that it has 12 or 13 universal skills, and spaces for some fill-in-the-blank skills. It is setting and genre neutral. https://cogentroleplay.com/

Incidentally, the Dungeons & Dragons 3rd edition System Reference Document (SRD) is available online. It is in essence the entirety of the 3rd edition players handbook. https://www.d20srd.org/

Lamentations of the Flame Princess (LotFP) is a retroclone of D&D Basic with a horror aesthetic, and indeed, it might even be a horror game disguised as a fantasy game. There are enough changes to its rules to make it distinct from other clones of D&D Basic such as Basic Fantasy RPG and Olde Swords Reign. https://www.lotfp.com/RPG/

Now for games I haven't actually played or read. 

I have read or played all of the games above, but I haven't touched Stars Without Number which is a sci-fi game. Including it because of how much I hear about it. https://www.drivethrurpg.com/en/product/230009/stars-without-number-revised-edition-free-version

Ironsworn is another game I've heard or read about that is inspired by older D&D, but I've also read that Ironsworn can be played in either a group or Solo? https://tomkinpress.com/collections/downloads-for-ironsworn

I've heard of Cepheus RPG which is another Sci-fi game. I haven't touched it, but I'm including it because it has an online system reference document (SRD). It's supposed to be compatible with Traveler, a popular sci-fi RPG. https://www.orffenspace.com/cepheus-srd/introduction.html

13th Age I'll add another game I haven't touched because it has a System Reference Document online: https://www.13thagesrd.com/