They used to have a website talking about the FLEET architecture, but it seems to have been taken down. Here it is on archive.org: https://web.archive.org/web/20120227072220/http://fleet.cs.b...

Edit: the page cited above has these links, but I should explicitly call the slides they call the best introduction to Fleet [1], and a page full of memos [2]

[1] https://web.archive.org/web/20120227072220/http://fleet.cs.b...

[2] https://web.archive.org/web/20120227072220/http://fleet.cs.b...