Twinity (download, Facebook)
When you start Twinity up it'll go through a number of updates and you'll see a map of the earth in the background. Once you get logged in it takes a little getting use to. The boxes you see everywhere labeled with the Twinity logo are more than just boxes. If you stand around long enough or if your internet is fast enough they'll load into objects like furniture. The controls are a tad problematic and navigating your avatar around objects is challenging since I ended up getting stuck between a coffee table and a chair. Another problem is that the camera is a bit awkward and doesn't automatically re-align itself behind the avatar. As for the outdoor environments, Twinity explains that they'll work more on that later hence the reason looking outside seems pretty bland.
Graphics (anti-aliasing capapable):
The graphics in Twinity are pretty decent (I saw steam coming off the water in the bathtub) and, just like with the new Release Candidate of SecondLife, you can enable anti-aliasing so the graphics aren't jagged. As for the character animation, um well watch your avatar's eyes. They don't blink properly but I'm sure it's just a temporary bug in the system, if you're wondering the eyes bulge out like bug eyes then go back to normal.
Vivaty (download, Facebook, Facebook App)
Right now the only place I've used this is on my Facebook profile.
Graphics (anti-aliasing capable):
The avatar walking animation is slightly out of step with the actual movement of the avatar which can be a tad irritating. Not only that but when you switch to the first-person view you can tell it's not really first-person, it only appears to only be. Screw around enough with the camera and you'll know what I'm talking about. Otherwise the environment is well done and you have fairly large selection of decent stuff to populate your scene with.