The entire system is made of a few main pieces. At the heart of the system is the summit server, which runs as a deamon (background, coordinating program) on each computer part of the summit system. It can talk with the summit file servers and security servers, and any summit cients. A summit client is built through the API.
The summit server exports a programmable API, so that clients can be written and then easily moved across systems. The API is available in several languages, so you have flexability over how you want to build your clients. This API gives you access to all of summit's functionality, such as file access, process invokation, system grouping, sharing of memory and IPC.
With the summit system installed, you can think of any machines as being part of one heterogeneous system. Given the permissions, you can run process anywhere, access any files, group machines and process such that they can perform distributed tasks or simply operate in a tighter manner, passing messages and sharing memory. All this is available without having to move all systems to one particular operating system and without being anchored to one language. Summit allows you to keep whatever systems you'd like, and simply use a single server to provide a generic layer with protocols that every other system will be able to understand.