Finally, there is an open source ASP.NET MVC based CRM product in a .NET world. The product is named Coevery, which means to connect everything.
As a late CRM product, Coevery has some late-developing advantages, especially adopting very modern techlogies. Like: Signle Page Application (SPA), Responsive Design, ASP.NET API, etc.
We hope that Coevery could help you. Of course, we more expect your opinion, even contribution.