I'll let the description from the web site do the talking...

“Velocity” is a distributed in-memory application cache platform for developing scalable, available, and high-performance applications. Using “Velocity,” applications can store any serializable CLR object without concern for where the object gets stored because data is cached across multiple computers. “Velocity” allows copies of data to be stored across the cache cluster, protecting data against failures. It can be configured to run as a service accessed over the network or can be run embedded with the distributed application. “Velocity” includes an ASP.NET session provider object enabling storage of ASP.NET session objects in the distributed cache without having to write to databases, which increases the performance and scalability of ASP.NET applications.

You can check out CTP 1 here.