Seal is my favorite app to demonstrate the power of installing apps outside of Google Play

Are you specifically looking to self-host? These are a few open source and self-hostable projects I’ve been keeping an eye on:

• Discourse for forums
• Stoat for real-time chat (similar to Discord)
• Vikunja for project management / kanban boards (more features than Trello, but simpler than Jira)
• Forgejo for code collaboration (similar to GitHub)