A repository of well known FOSS is located at dotnetit.org. This includes Apache Xerces (an XML parser including DOM and SAX implementations), Apache Xalan (an XSLT and XPATH parser and processor), regexp libraries, cryptography libraries, etc.

An open source alternative .NET IDE is #develop. This project is coming along fast, and includes a library NRefactory that parses C# and VB.NET and IMO has a superior abstract syntax tree model than the CodeDom.

If broken it is, fix it you should is a great MSDN blog heavy in content that walks through debugging techniques for memory leaks, crashes and the like, using windbg and perfmon. Great place to learn how to poke around your heap from the command line.

The standard corlib doesn't provide a good library to creating zip files (while it does do zip compression). If you'd like to do this but don't want to use a third party check out Jon Galoway's blog. In short, use the J# library and java.util.zip.

I've branched the code, and pulled out the stuff I've been thinking about to set free (as in speech). This is basically just the raw bridge, no "generic object embedding". Check out the project on the codeplex project page or on freshmeat. Future enhancements for this piece will include the debugger API, and not much else I can think of right now. More updates to come as I settle down (I've just relocated from NYC to LA).