I don't know of very many implementations of URIs. Dan Connolly keeps a list of notes on implementations.
C coders can use LibWWW implements a number of URI functions (HTParse, HTEscape).
Java* has an implementation by Christian Niles. In addition, Justin Couch* has written a URI resolver and a URN resolver.
Perl* has a number of URI modules by Gisle Aas*. There's also related stuff in other modules.
Python* comes with urlparse and urllib and Mark Nottingham wrote URL normalization routines.
TCL* folks can use the implementation I wrote for my hacking.
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