From the Sold dept.:
Raindrop is a new exploration by the team responsible for Thunderbird to explore new ways to use open Web technologies to create useful, compelling messaging experiences.

Raindrop's mission: make it enjoyable to participate in conversations from people you care about, whether the conversations are in email, on twitter, a friend's blog or as part of a social networking site.

Raindrop uses a mini web server to fetch your conversations from different sources (mail, twitter, RSS feeds), intelligently pulls out the important parts, and allows you to interact with them using your favorite modern web browser (Firefox, Safari or Chrome).

mozilla.com/raindrop