Web-based social bookmarking system. Allows multiple users to store, share and tag their favourite links online.
#del.icio.us
Meshly
IM-based digg+del.icio.us bookmarking/voting system.
trailfire
Online tool for creating webpage trails and sharing them, plus sharing bookmarks.
Visualizing Del.icio.us Roundup
Visualizing Del.icio.us Roundup
Soooo meta, a list of del.icio.us visualization tools, tagged using del.icio.us