I've always wanted a 'Wikipedia for formal proofs'. It's never materialised though, sadly.

I would've expected such an online Encyclopedia to form around Coq or Isabelle/HOL, as these languages/assistants seem to be the most popular.

Unfortunately, I've never seen enough momentum behind one proof language to give a wiki a chance of becoming something substantial.

It seems the formal proof community (which is already small) is so spread out over several languages, that it's hard to get the fire burning.