What does aspnet_regiis.exe do

My favorite feature of it, is the ability to encrypt settings in web.config something along the lines of:

aspnet_regiis -pe /myapprootvirtualdirector

and decrypt is -pd

encrypt only after deployment to the server - as encrypting on one machine won't be valid on the other unless you share machine keys.

From MSDN reference:

When multiple versions of the .NET Framework are executing side-by-side on a single computer, the ASP.NET ISAPI version mapped to an ASP.NET application determines which version of the common language runtime (CLR) is used for the application. The ASP.NET IIS Registration Tool (Aspnet_regiis.exe) allows an administrator or installation program to easily update the script maps for an ASP.NET application to point to the ASP.NET ISAPI version that is associated with the tool. The tool can also be used to display the status of all installed versions of ASP. NET, register the ASP.NET version that is coupled with the tool, create client-script directories, and perform other configuration operations.

From Scott Forsyth's blog:

Starting in the first version of ASP.NET, Microsoft has provided a tool to control which version of the framework is registered in IIS. This tool, aspnet_regiis.exe, is quite flexible and with the right understanding of how IIS and ASP.NET work, can be used for most any situation.

It reg isters ASPNET extensions with IIS.