He says he's going to write his own mail server. I use SQLite all the time, and I'm going to try Fossil when I get a bit of time to dig into it. I will definitely give his mail system a look when it's out.
I did it mostly for the built in project management (wiki, bug tracking), and to get away from the big SaaS environments. But the sqlite binary file repo sold me on the architecture quickly.
Dr. Hipp is a fantastic software engineer and product designer. Both SQLite and Fossil do what they need, have only the bells and whistles needed, and have clean, consistent designs. I've browsed the source for SQLite before, and it's also clean, legible, and quality.