An open-source project that I pay a bit of attention to is SOGo, aka “scalable OGo”. It’s a project w/ a long history, much of which I don’t know well, but what’s interesting to me is that they’re trying to be the Yin to Thunderbird’s Yang. SOGo includes a web frontend, which is designed to look like Thunderbird, which is a fascinating choice.
The folks at Inverse, who are the primary drivers of SOGo, as far as I know, are also doing Thunderbird & Lightning add-ons (SOGo Connector and SOGo Integrator), including adding support for CardDAV, Free/Busy, etc. They’re also helping with patches to Lightning, for which we’re definitely grateful!
SOGo reached the 1.0 milestone yesterday, which is always worth celebrating. If you’re interested in the groupware space and looking at software that plays well w/ thunderbird, check it out.