It's only the first draft, but Linden Lab (specifically Mark Lentczner aka Zero Linden) has published the awkwardly named Second Life Grid Open Grid Protocol (SLGOGP) on the Second Life wiki.
While very preliminary and far from complete, the SLGOGP is essentially the beginnings of the technical underpinning that will ultimately allow the cohesive operation of both Linden-operated and non-Linden-operated Second-Life style simulators and grids.
If you're not deeply excited by protocol documents, this is probably not going to be your cup of tea. Otherwise, if raw technical protocols get you hot, this is a great starting point for technical discussion.
