The Yahoo Site Explorer tool will be shut down as of this Monday November 21st. Yahoo made the announcement today on their Yahoo! Search Blog. This marks the completion of "merging" the Site Explorer tool into the Bing Webmaster tools. The brief yahoo blog post reads:

With the completion of algorithmic transition to Bing, Yahoo! Search has merged Site Explorer into Bing Webmaster Tools. Webmasters should now be using the Bing Webmaster Tools to ensure that their websites continue to get high quality organic search traffic from Bing and Yahoo!. Site Explorer services will not be available from November 21, 2011.

The Bing webmaster tools has most of the data with the major exception of competitors backlink information, which made it an important tool for many SEO professionals.

Fortunately there are alternatives, although not directly provided by search engines. Majestic SEO and SEOmoz both offer an insight into competitors link-building stratergies. 

Just like the Yahoo Site Explorer was built into browser extensions, basic back-link statistics can be viewed free with a Google Chrome extension called "SEO for Chrome", which integrates Majestic SEO data. This extension provides a quick snapshot of other SEO indicators like Google indexed pages and Pagerank.

What are your thoughts on these alternatives? Can you suggest other tools?