I want to host multiple web sites (all with different domains - not sub domains) with the same ASP.NET MVC app. I need the app to act differently based off the domain, but
ASP.NET MVC Domain Routing demonstrates one possible way to control ASP.Net MVC application behavior based on the domain name that was used to reach your site.
This should be possible with IIS using the host headers field in the bindings settings. You can add as many different host headers as you want for your application. And as long as that domain somehow goes to that host on that particular port (http or https or custom), then that application will be used.