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!

I haven't played Stoneburner yet, but I ran a 10 session campaign of Tales of the Burned Stones (the free fantasy version released as a reward from the Stoneburner Kickstarter), and it was super fun! If you get a chance I highly recommend bumping Stoneburner up in your queue.