Planka
planka.app
Open-source, realtime kanban board — a self-hostable alternative to Trello for visual task and project management.
Why it is useful
Planka replicates Trello's card-and-board workflow (drag-and-drop, labels, due dates, attachments) with realtime multi-user updates, and being self-hosted means no board or card limits tied to a paid plan. It's a lightweight option for teams that just need Trello-style boards without a SaaS subscription.