Alternatives to IIS for Windows to run ASP.NET
There is UltiDev Cassini which is a "free, light-weight and redistributable web server that can host ASP.NET 3.5, 3.0, 2.0 and 1.1 applications and static HTML sites". (It is based on the original Cassini web server).
Other than that, there is the development web server, which comes with Visual Studio. But as far as I know, this can only be used during development/from within Visual Studio.
p.s. UtilDev PRO supports asp.net 4.0.
Apache 2 can do this I think. At least it can while running on Linux.
You will need a plugin for it though. Mod_aspdotnet is your friend :-)