I’d like to start collecting information about cool email experiments. To jumpstart the discussion, here are a few of my favorites:

• IBM’s Remail project is inspirational.
• Ka-Ping Yee has a tendency to come up with cool stuff, from nosy lists in Roundup to thread maps and user-directed screen reading
• Andrew Sutherland is doing cool visualization experiments, including with Thunderbird
• GNUmail is a project Andrew mentioned which I need to read up on.

What other projects should I know about?

[UPDATE: Please don’t just suggest mail clients — My mention of GNUmail sent people astray, as I forgot to mention that it was notable because it implemented the arc-threading view. I’m not interested in an inventory of wholesale mail clients — only an inventory of specific features, or even better yet, not-yet-feature-but-ideas which show innovation and promise]