A widget is a small pretty looking self contained program that runs on the desktop and performs a specific function. There are weather widget that fetches up-to-date weather forecasts and information from the Internet, clock widgets that displays the time, calendar widgets and all sorts of widgets that can perform a wide variety of tasks. Widgets require a platform to run and there are several available for both Windows and Linux. A lot of users are already aware of the various options available for Windows, but Linux widgets aren't that popular. So here I'm going to present some of the best widget engines available for Linux.
1. Screenlets: Probably the best looking widget platform available for Linux. The widgets are cute and very similar to those offered by Yahoo and Apple.
2. SuperKaramba: One of the most popular widget engines for the KDE desktop. The widgets are referred to as themes. There are plenty to download at kdelook.org
3. gDesklets: Another very nice looking widget engine. gDesklets is not restricted to one desktop environment, but currently works on most of the modern Unix desktops (including GNOME, KDE, Xfce). The support for a wide variety of desktop enviroment is a very helpful feature of gDesklets.
4. aDesklets: adesklets is an interactive Imlib2 console for the X Window System. It provides to scripted languages a clean and simple way to write great looking, mildly interactive desktop integrated graphic applets. The collection isn't that great and won't find variety, but desklets for popular tasks are available.
5. Moonlight Desklets: Moonlight is Novell's nascent open-source implementation of Microsoft's Silverlight framework for rapid, rich media application development. This is a relatively new engine so not many widgets are available. But they have some really nice looking widgets nonetheless.
6. Google Gadgets: Google gadgets come bundled along with the Google Desktop software. A very large collection of gadgets are available.
7. Opera widgets: Opera widgets run on top of the Opera browser (version 9 and above), the only browser that supports widgets. There are more than a thousand Opera widgets available.
8. Jackfield: Jackfield isn't actually a widget engine. It's an application for the Gnome desktop that can run widgets of other popular platforms like Yahoo, Apple, Microsoft Vista Sidebar and Opera. If you use this application you get access to thousands of widgets from all the 4 platforms!!
If you count them all, you will find that it's actually 10 and not 8 widget engines that you can run on Linux. Thanks to Jackfield, that enables you to run 3 of the engines that aren't supported in Linux.