Patchwork

Connect with friends without depending on any central servers.
Don't worry about spam, you only get messages from people you follow.
Use Patchwork online or offline, the data you need is stored on your device.
Sync messages with friends when you're on the same Wi-Fi network.
Keep secrets with private messages, which are always end-to-end encrypted.
Change and improve Patchwork however you'd like, it's free and open source.