RetroShare (Decentralized chat, email, forums, and file sharing)

RetroShare is a Open Source cross-platform, Friend-2-Friend and secure
decentralised communication platform. It lets you to securely chat
and share files with your friends, family and coworkers, using a
web-of-trust to authenticate peers and OpenSSL to encrypt all
communication. RetroShare provides filesharing, chat, messages,
forums and channels.

Note: RetroShare uses /usr/lib/retroshare/extensions/ to store its
plugins, against standard Slackware convention. RetroShare hardwires
this into the code. This build does not attempt to patch the source
code to fix this, though the maintainer welcomes patches to fix this
issue.