Microsoft's forthcoming Visual Studio Team System will include source code control, integrated defect tracking, testing, reports, and a bunch of other project management and project governance tools and capabilities. All built in and integrated. BUT! That does not mean that there are not other options, even open source options. AnkhSVN and Igloo are a couple examples of source code control add-ins for Visual Studio. NUnit covers unit testing. There are others, too! Here's a brief list, with some details:
All of the things I mentioned above are open source tools, or have source code available. Does it seem strange that Visual Studio works with them? It shouldn't.
Much of it is possible through the VSIP SDK, and the published extensibility interfaces for Visual Studio. For those tools that don't integrate into VS but rather into .NET itself, is it too obvious to point out that .NET Framework can be used on open source projects?
If you think it's strange that open source stuff works together with Microsoft commercial products, you may have been reading too many press releases from companies saying "Microsoft means lock in" and ".NET is a Windows-only proposition". Sure, Visual Studio runs only on Windows, but that doesn't mean your SCCS has to run on Windows too. It doesn't say anything about your enterprise database, or your queueing system, or your testing tools, and so on. Microsoft tries to encourage extensions of Visual Studio, specifically. Check out Dr Ex's page.
There are a number of other companion tools, too . Some free, some open source, some commercial. Some plug into VS, some are standalone. Some of my favorites are: Reflector for examining assemblies, CSAH for helping VS devs post their code on blogs, WSCF for contract-first webservices development, and the vsPropertyGenerator to help automate adding and removing properties on C# classes. The SharpToolbox has a very good list, organized by category.
Don't get me wrong, I believe there is real value in integrating the various "big block" pieces, and delivering a nice workflow, as Microsoft does with VSTS. But it won't make sense for everyone. Some people like their Subversion or their CVS (~shudder~). They want their NUnit, they like their CruiseControl. I say to those people: Good on ya. With Visual Studio you can keep using and exploiting the stuff you love. And, beyond the big blocks, there are lots of smaller add-ins and complementary tools that might come in handy in your environment.
What are you using?