I have set up a server 2008R2 with 5 licenses for RDS.
The application runs fine inside the network, but can not execute the app from outside the network.
The application is quickbooks enterprise 2011.
When outside the network, I can hit the webapp access page, and when I click on the app I get prompted for credentials but, every time i enter the credentials it just prompts me for credentials over and over again. Inside the network, it prompts and connects.
The server is in a workgroup since they do not have or need a domain, however if RDS requires a domain I can change that. I have not see anything indicating a domain is required.