I'm not actively working on it daily, as I have shortage of free time and helping hands, but the HTTP Spec Test Suite is my Moby-Dick. I wrote about it here: https://www.caffeinatedwonders.com/2024/12/18/towards-valida..., I also discussed it on the HTTP WG mailing list and presented it at the HTTP WG Workshop last year.
Another Moby-Dick of mine is Kadessh, the SSH server plugin of Caddy, formerly known as caddy-ssh. This one is an itch. I wrote about it here https://www.caffeinatedwonders.com/2022/03/28/new-ssh-server..., and the repo is here: https://github.com/kadeessh/kadeessh. Similar to the other one, feedback and helping hands are sorely needed.
They are both sort of an obsession and itches of mine, but between dayjob and school, I barely have a chance to have the clear mind to give them the attention they require.