The official site sends you to Amazon to get the book.
Dungeon Crawl Classics -- The name basically says it all. Still based on d20 system. Big honking rulebook. 5e players will probably like it, 3.5e players usually do not. This is due to the perceived unfairness of the game by some. The game also uses non platonic solids, in addition to platonic solids, so you would need extra dice. They're cool and fun to roll though. A set for the table is enough. They public tons of adventures and have some well known ones, like Sailors on a Starless Sea. They are all very good though. They have been doing adventures since the early 2000's and have it down to a production. Also, they're not afraid of the chainmail bikini -- written by a woman, no less!
Warhammer Fantasy Roleplay and Zweihander -- the latest WFRP just came out and I haven't played it. But they're redoing the enemy within, and that is seriously one of the best campaigns in gaming. Damned good. Zweihander is WFRP without the warhammer setting. I would play Zweihander if the group wasn't savvy with the old world, or I wasn't. Too much lore to deal with. Anyway, dark fantasy, late-medieval quasi Europe. Really cool. You can be a ratcatcher and have a dog.
Castles and Crusades -- This game feels like 2e to me without the bad rules. Pretty well supported. Very tight mechanics. This can do everything DnD can do. And 5e took from this pretty liberally, I believe. Also, the owner, Gary, sent my friend some books completely for free when he was deployed to Iraq a decade ago. No questions asked, he just wanted his APO address.
There's a bunch of other systems, but these are the ones I'd play today if I wanted a fantasy alternative.
Sure, so 2nd edition can be found here.
https://www.drivethrurpg.com/m/product/62847
That's 2nd edition of Warhammer Fantasy Role Play which is one of the 4 official pen and paper roleplaying games set in the Warhammer World.
4th edition is the new edition that came out recently and has become popular amongst long time fans of the game. You can find information on that one here.
https://www.cubicle7games.com/our-games/warhammer-fantasy-roleplay-2/
I play 2nd edition but it is older and no longer supported so nothing new is coming out for it. So if you'd like something a little more alive with active development then look at 4th edition. Otherwise 2nd edition has had a very strong following for years and years and tons of people around here still swear by it.
If you want other grim dark games then here's some suggestions that I personally really love.
My favorite by far would be a game called Zweihander. It was made by a really great guy who put a lot of love into his 2nd edition homebrew and eventually published it as its own game. Definitely worth checking out.
https://www.amazon.com/ZWEIHANDER-Grim-Perilous-RPG-Rulebook/dp/1524851663
If you're looking for something that might be more familiar to your D&D roots you can check out a game called Shadow of the Demon Lord. It is a grimdark game with tons of flavor in it's game mechanics. It's a lot darker than dnd is but still uses the d20 system, that is, you make most of your rolls with a 20 sided die, as opposed to the other games I mentioned which all use a d100 system of percentile rolls. Both work great it's just a matter of preference that you might find you like one over the other.
https://www.drivethrurpg.com/m/product/155572
Hope this helps get you on the right track! Let me know if you have any questions.
As others have said, there's an official The Witcher ttrpg. It has a free quickstart too, which lets you try it before you buy it.
Warhammer Fantasy RP would also work well for it, indeed, though you'd have to homebrew a bit. Personally, I'd pick the 2nd edition of the game, but you could try its first or its most recent 4th as well. 3rd, not so much, imo.
You could also use Zweihänder, which is a kind of a 3rd party clone of WFRP.
Chaosium's Basic Roleplaying (which also has a free quickstart) could also handle this well, with some homebrewing. (It's the engine behind games like Call of Cthulhu.)
Finally, if you're looking for a fast solution, I'd recommend taking a look at The Black Hack (its entire text (1st edition) available online for free under the OGL) You'd need homebrewing, but considering how brutally simple and streamlined the D&D like system is, it could probably be done in an afternoon.
There's a Warhammer FRP clone called Zweihänder which is actually surprisingly cheap for how bonkers huge and quality the book is.
Almost 700 pages, soft-matter hardcover, ribbons, the works...
There's Warhhamer FRP clone called Zweihänder which is actually surprisingly cheap for how bonkers huge and quality the book is.
Almost 700 pages, soft-matter hardcover, ribbons, the works...