Here’s my quick, two sentence definition of Indigo in order to give you an idea about the scope of this thing:
Indigo is the successor technology and the consolidation of DCOM, COM+, Enterprise Services, Remoting, ASP.NET Web Services (ASMX), WSE, and the Microsoft Message Queue. It provides services for building distributed systems all the way from simplistic cross-appdomain message passing and ORPC to cross-platform, cross-organization, vastly distributed, service-oriented architectures providing reliable, secure, transactional, scalable and fast, online or offline, synchronous and asynchronous XML messaging.