Nunit - and open source

one of my friend asked me about Nunit, it that a framework or not,
i told him it is a unittesting framework.
and it contains a dll , which we need to include in our test project and compile the test project.
and tools included are nunitConsole which helps us to run the unit testcases in the console mode.
and NunitGUI which is used to run the testcases in the GUI mode.

and Nunit can be integrated with the Build task , and can be put in the build server and use cruise control.net to execute the testcases .

Iam a fan of microsoft. but i dont like the strategy microsoft follows.
for instance , it has developed its own unit testing framework. which can be executed inside the visual studio.

but the visual studio testcases can also be executed with the nunit.

Due to the fast change of framework (dotnet), the open source documentation tool died.
and microsoft has introduced a new tool which is known as SandCatle.

i dont know whether it is possible to execute the Unit testcases written using Visual studio testing framework, can be executed without installing Vs.net.
(ie) i use Visual studio to develop the testcases. compile the dll and run them in the dll without visual studio.
my question here is whether microsoft providing any free tool to execute the testcases without Nunit.