Plume 
Federated blogging engine, based on ActivityPub. It uses the Rocket framework, and Diesel to interact with the database.
It is not yet ready for production use, but we have all the basic features (account management, blogs, articles, comments, etc) and a basic federation.
Feel free to join our Matrix room: #plume:disroot.org to discuss about the project!
If you are interested in coding, check out the development guide. You can also help by reporting issues, suggesting features, or writing documentation for instance.
If you would like to help by translating Plume, we also have a guide for you!