Velocity was the code name for a distributed key-value cache platform for in-memory caches spread across multiple systems, developed by Microsoft. It is now incorporated as the caching element of Microsoft's AppFabric.
Design
Any number of systems can be a part of the cache; the velocity runtime pools together the individual caches on each machine to present a unified view to the applications. Applications need not know on which machine the cache is stored; rather the applications query the Velocity runtime which in turn, forwards the request to the system that houses the cache item. The Velocity API is surfaced in managed code; so any CLI-compliant language can be used to access the Velocity cache. Any serialized managed object can be added to the cache.