Today the BCL Team is launching a CodePlex site to host samples, previews, and prototypes. You can find it at http://bcl.codeplex.com.
This is a site for the BCL Team to get features to customers to try out without requiring a Beta or CTP of the .NET Framework. Our goal is to put generally useful functionality on the CodePlex site, and to get feedback on it and have the chance to iterate on the design. Having a feature there does not mean that it will eventually end up in the BCL. Some items are samples that build on top of existing classes, and some features might be ones we were considering for the .NET Framework but decided not to include for one reason or another.
We'd love to get your feedback in the form of comments, bug reports, and feature requests, but please note that we cannot take code submissions. We plan to release updates with new features and updates to existing features on a quarterly basis, but we're just getting started with this and may adjust our schedule depending on how things go.
And just to avoid confusion, you will not find the source code for the whole BCL on this CodePlex site. The site is for things we're thinking about for the future, not our existing classes.
The first four projects up on the site are BigRational, Long Path, PerfMonitor, and TraceEvent. Go check them out and let us know what you think.