I've noticed quite a few projects being open sourced lately that I thought I'd point out:
Protocol Buffers are a heavily used inside Google as a data interchange format. They're beautiful. Generated classes for C++, Java and Python that output very compact binary data that parses very quickly and can be backwards compatible across revisions of your data structure. Here's the blog post.
Google C++ Testing Framework
I don't know a whole lot about this since I don't write C++ but it sounds pretty cool. Who wouldn't want to write "death tests". Here's the blog post.
AdWords API Starter Kit
This project aims to help advertisers get started easier with the AdWords API (my manager played a big role in developing this). There's a blog post that explains it on the AdWords API Blog.
Unfortunately tools you use go out of support from the companies that built them. Google's BrowserSync now falls into this category. Thankfully the team has open sourced the project however there's still the minor sticking point of where will all of the data be synced to? Here's the blog post.
If you're a Mac user, use Google Docs or Google Bookmarks and use Spotlight this will be of interest. This tool will let you index Docs and Bookmarks and add that into your Spotlight index for easy searching of data on your computer and data at Google. Here's the blog post.