The goal of Jazz Foundation Project ( through Jazz Integration architecture ) is to provide data and services through resource oriented web services.

These web services use URIs, HTTP methods, and XML and JSON, that work like the rest of the Web. The protocol is stateless; client state is carried in the client; server state is explicitly reflected in the resources.

Please take a look at https://jazz.net/projects/jazz-foundation/

While not all possible services and data is available through REST web services right now, its progressively becoming available and sooner or later most of it would be available.

So you should be able to write a client in any language including C# or VB to consume the data or invoke these services.

-Sandeep