Tiny Core also runs from ramdisk, uses a packaging systems based on tarballs mounted in a fusefs and can be installed on a dos formatted usb key. It also has a subdistro named dCore[1] which uses debian packages (which it unpacks and mounts in the fusefs) so you get access to the ~70K packages of debian.

It's documentation is a free book : http://www.tinycorelinux.net/book.html

[1] https://wiki.tinycorelinux.net/doku.php?id=dcore:welcome