There are a number of open source web apps that are based around "kan ban" which is similar to Trello in approach. A few are:
- Kanboard https://kanboard.org/
- WeKan https://wekan.github.io/
- Taiga https://taiga.io/#Features
There are more out there if you search for "open source kanban" or "open source kan board".
I've noticed that some communities will just not show up when I search hereon fedia.io. !fountainpens@sopuli.xyz is one of them. No matter how I search for it, I can't seem to find it here. Other communities from Lemmy seem to be no problem, so it's odd.