It's a fully fleshed out Kanban board system, similar to Trello. I like it more than Trello because it is free, open-source, and self-hosted (meaning my data stays my data). It also looks much better and more professional in my opinion, where Trello looks somewhat childish.

Essentially an open-source clone of Trello, although in some ways it is starting to branch off by itself now. Since you have control of the database and underlying code, it's quite easy to import, export, and back up your board data, which is very important. While Trello does have export functionality, it's marred by the fact that there is basically no way to import it back.

Wekan is very reponsive. Everything happens happens instantly and the immediate feedback is great. It's very much modeled after Trello - they even use some of the same words for the concepts inside the app.