I'm having a hard time tracking down potential licensing issues with SharePoint Foundation if it's used internally (free with appropriate CALs), but pulling data from it with an asp.net app and using it externally. I can't seem to find anything that addresses this. Would we need an External Connector even if users don't hit SharePoint directly?
I contacted MS and here's what they said:
Foundation Licensing: we need an External Connector license if the users are not anonymous, no licensing for SharePoint Foundation necessary if the users are anonymous. They said we'd need the usual Windows Server License for web exposure and the per-proc SQL Server License. I hope that helps others in the same situation. I'd still confirm with MS if you're planning on doing this, though, it could change.