Mono
The revised version of Second Life's scripting virtual machine is based on Mono, the open source implementation of the Microsoft.NET framework. The Mono VM was introduced to several simulators (sims) on the Second Life Beta grid for compatibility testing on 29 January 2008 and later that year on 20 August 2008 Linden Lab started deploying it on the production grid - with the entire production grid updated to use it on 29 August 2008.
While the LSL scripting language remained the same, scripts executed on the Mono underpinnings were up to 220 times faster in execution, but at the cost of a somewhat higher overhead when creating (rezzing) scripted objects and moving them from sim to sim.
Read more about this topic: Linden Scripting Language