A tool to patch Celeste to remove the framerate cap
Download the latest release, then run it in a terminal, passing the path to Celeste.exe. Make sure the game is closed before running the tool. You'll also probably want to enable vsync to limit the game's framerate to that of your monitor.
Once patched, the program doesn't need to be rerun unless the game is updated or redownloaded.
Windows
CelesteUncapped.exe "C:\Program Files (x86)\Steam\steamapps\common\Celeste\Celeste.exe"
Linux
mono CelesteUncapped.exe ~/.local/share/Steam/steamapps/common/Celeste/Celeste.exe