Rather than repeat things already mentioned, I'll suggest a few that my group has played and enjoyed.
Barbarians of Lemuria. Barbarians, thieves, sorcerors and all that in a more imaginative setting than most, fairly simple system, not much support for it.
Conan: Adventures in an Age Undreamed Of. Modiphius, uses their 2d20 system, one of the more complex games in that system, I imagine most people are familiar with Hyboria if they're reading this. Lots of stuff for this.
Questworlds. Very generic, much more abstract than most of the systems that have been mentioned, It can run pretty much any setting, quite a bit of work for the GM, probably something that depends a lot on players "getting it". Still not officially released but a free version is up on itch.io
Sword of Cepheus. Derived from Cepheus Engine, a Traveller clone. There's a fair number of adventures for this or related games, largely skill based and characters will be more fragile than experience D&D ones.
Forbidden Lands. One of the excellent free League games, explorers and plunderers in a land of ruins, simple system, build a base, establish your presence, and probably die nastily. Some supporting adventures and a new campaign region so far, more on the way it seems.