I love ansuz's and cjd's work on CryptPad! I use it daily as my personal notes wiki synced between 3 computers, and occasionally for collaborative notes taking in video calls with ~15 people. My happiness levels have increased with every new iteration of features and fixes.

I recently suggested to add a frontend for collaborative agile retrospective boards, similar to Retrium. CryptPad seems pretty pluggable in that regard, and actually TIL it can even edit presentation slides now :)