Omega Online is cross-platform peer-to-peer middleware for home computing. The project provides tools and libraries to author distributed computing in a language-neutral manner, using open standards.
The Property Set Library (PSL) is a template-based C++ container library providing value observation, event calling, garbage collection, serialization, object persistence, reflection, thread-safety and other accompanying features.
The CoreLibrary is a multiplatform object library for C++ (Linux, Win32, MacOSX, PocketPC). It provides many of the common objects found in Java (Strings, Threads, Collections, etc.) and has the ability to send objects across the network like CORBA.
Dotlife is a very simple open source framework for C++ distributed objects. There are no advanced features but just a focus about how object can communicate in a distributed manner. Dotlife has also a minimal support for unit testing.
ACDK - Artefaktur Component Development Kit - is a platform independent C++-framework similar to Java or C#/.NET for generating distributed and scriptable components and applications.