Is there an equivalent in .NET to a websphere-style app server? Something that will manage all our WCF endpoints across multiple projects/solutions, track dependencies and versions, handle WS-Discovery (or WSDL or whatever)?
Ideally something F/OSS?
If you are running WCF, you probably also are using Windows Server 2003 or 2008. The appserver type features in the .NET world are spread across IIS, MSMQ and COM+, which are bundled with the server, so free as in no additional cost after the server, but not necessarily free as in code you can read and modify.
These are two more opensource app servers for .NET Base4 http://en.wikipedia.org/wiki/Base4_Application_Server TNAPS http://en.wikipedia.org/wiki/TNAPS_Application_Server
Also, WCF is capable of speaking standards, so I suppose you could have a .NET WCF client invoke/send messages to JBoss, however, the rumor is that for all products of this sort, you get the best results from using a homogeneous stack-- the standards are good but not perfect.