In a blog posting this week, Google has announced the closure of a number of products and projects, including Google Gears, Knol, and Renewable Energy Cheaper than Coal, which the company says haven't had the impact they had hoped for.

The announcement is the third such announcement by the search giant in the last three months.

“To recap, we’re in the process of shutting down a number of products which haven’t had the impact we’d hoped for, integrating others as features into our broader product efforts, and ending several which have shown us a different path forward,” wrote Google Senior Vice President of Operations Urs Holzle in the blog post.

Among the Google casualties announced this week:

Google Bookmarks Lists — An experimental feature for sharing bookmarks and collaborating with friends will end on December 19, 2011. All bookmarks within Lists will be retained and labeled for easier identification, while the rest of Google Bookmarks will function as usual.

Google Friend Connect — a feature that let webmasters to add social features to their sites. Service ends for all non-Blogger sites on March 1, 2012.

Google Gears — In March Google said goodbye to the Gears browser extension for creating offline web applications and stopped supporting new browsers. On December 1, 2011, Gears-based Gmail and Calendar offline will stop working across all browsers, and later in December Gears will no longer be available for download.

Google Search Timeline — a graph of historical results for a query. Users will be able to restrict any search to particular time periods using the refinement tools on the left-hand side of the search page. Additionally, users who wish to see graphs with historical trends for a web search can use or for data since 2004. For more historical data, the "ngram viewer" in Google Books offers similar information.

Google Wave — The company announced it had stopped development on Google Wave over a year ago. On January 31, 2012, Wave will become read-only and on April 30 it will be turned off completely.

Knol — launched Knol in 2007 to help improve web content by enabling experts to collaborate on in-depth articles. Ends April 30, 2012. Users can download their knols to a file and/or migrate them to

Renewable Energy Cheaper than Coal —This initiative was developed as an effort to drive down the cost of renewable energy, with an engineering team focused on researching improvements to solar power technology. Google says that other institutions are better positioned than Google so they have published their results and closed their efforts.

Other notable shutdowns announced in September and October include Aardvark, Code Search, Desktop, Google Pack, Jaiku, Notebook, and Side Wiki. See the following Google blog posts for details on these products ( A fall sweep and A fall spring-clean )

Discuss the Google shutdowns in Digital Home's On the Web Forum .