Y! Backlink Counter is a Javascript tool that enables the user to check the number of web pages that contain (at least) a link to a given URL address. It uses the service provided by Yahoo! Site Explorer.
Results are shown in the Yahoo! Badge, if the user clicks on it a Yahoo! Site Explorer web page is opened, containing a list of all the referring links (aka inlinks or backlinks).

Opera Widget

Opera widget screenshot

Y! Backlink Counter Opera Widget can be downloaded from the Opera Widgets website. Javascript required.

Google Gadget

Google Gadget screenshot

Y! Backlink Counter Google Gadget consists of markup code (HTML) and Javascript code, contained in an iframe (to avoid "cross-site scripting" threats).

The gadget can be embedded in an iGoogle page or in any web page.

Y! Backlink Counter Google Gadget can be found on the Google Gadgets directory. Javascript required.