KDE, a desktop environment for Linux will support the HTML Canvas element in the next release (KDE 4). What does this mean to you, the user? The KDE Team's goal is to run Apple Dashboard Widgets on Linux!
Widgets themselves are nothing special. Having developed one and dug through, modified, and working on more, they are just a collection of HTML and Javascript that happens to show up very nicely in a big dynamic webpage called Dashboard
This will be nice since currently only KonfabulatorYahoo! Widgets are cross-platform.