So,
I've been working on something for the last day or two (
would have got it done faster, but someone demanded I go to bed last night. 
)
The goal is to produce something you can embed in a web page or website and like the Lively client people can just browse into the world and access a subset of features sufficient to visit it.
If you are interested in the technical specifics, I wrote up two posts on it.
Here and
here.
I could use some help though - to do accurate primitive rendering, I need to rely on a piece of code LL have been promising to release for a while now.
While I can use the simplified "meshmeriser" we developed to compensate for OpenSim's physics engines - rendering in the viewer is a bit more complex since we need UV coordinates and the meshes to look identical between the viewers, and to get things identical, we need to use the same routines - using the approximations (while more efficient) wont work as well in this case.
There's a Jira issue to get LL to release the bits under a more usable license and I'd really appreciated if people can vote on that one (It's already in the top list of issues, but it's been 6 months since a linden commented on it).