I found another free clone of del.icio.us, yesterday. It's called Scuttle and is written in PHP instead of Perl (as is the case with Rubric, the code behind de.lirio.us/). Also, Scuttle is GPL'd whereas Rubric uses the Artistic lincense. As of version 0.2.0 Scuttle supports the del.icio.us API.
I'll probably try out Scuttle on this site soon, to find out how useful it is and how it works.