I use this one, and it’s pretty nice: https://weasyprint.org/. They implement their own rendering engine so its support of new features and edge cases isn’t the best, but every problem I’ve run into with it has been solvable with a little work. I really like it for laying out printed forms!

The big one was its complete lack of mobility abilities or ranged attacks, so a party with overland flight could attack it pretty much with impunity. Iirc that was most commonly paired with shrinking a bunch of boulders, carrying them up with you, then dropping them right as the shrinking spell expired. This is all from memory 15 years ago though so details could be a bit sketchy.