Continuing my travels to OpenSim-based virtual worlds, we come to two worlds that aren't for general use, but are very important nonetheless: Meta7 and ScienceSim.
Meta7 is a world showcasing an innovative technology called LightShare. LightShare allows region owners to share their WindLight environment settings with users via LSL script. Aside from LightShare, Meta 7 sadly doesn't offer much beyond most other OpenSim worlds. However LightShare alone makes it at least worth a look, especially if you're an OpenSim admin or a viewer developer looking to spice up your grid/viewer.
ScienceSim is for those who wish to use OpenSim for scientific and bleeding-edge research, simulation and education. The uber-geek's virtual world, if you will. If "Fern Lifecycle and Population Genetics Simulations" are your cup of tea, then ScienceSim is right up your alley. Just be sure to change your starter avatar's chin if you choose the male starter avatar(unless you're Jay Leno).
There may be a part 3 soon, but in the meantime I highly recommend taking a look at the grid list at Hyperica, as there's a heck of a lot more grids out there than I could realistically travel to.