The Opera web browser has introduced a Dashboard-like Widget feature in Opera 9 Preview 2*. I believe this is the first 3+ platform widget framework out there.
Dashboard is, of course, Mac OS X only. Yahoo! Widgets (formerly Konfabulator) is Windows XP and Mac OS X only. The KDE Desktop (mostly used on Linux and *BSD) has plans to include floating applets in KDE4’s revamped desktop, Plasma. Opera runs on Windows, Mac, Linux, and a number of other platforms.
Yahoo widgets are a completely separate XML format, but it looks like it should be possible to build a widget that works on both Opera and Dashboard, or at least one you can convert easily to two downloads.
- Opera Widget Howto*
- Dashboard Widget Howto**
- Yahoo Widget Howto**
*Original links dead, but copies found at the Internet Archive.
I belive there are more than three.
Opera Widgets, Microsoft Gadgets, Apple’s Dashboard, Google’s Widgets and Yahoo! Widget Engine (Konfubulator).
Wow. Aside from general links to Opera & KDE, this old post about desktop widgets has ONE working link left.