Dolphin Viewer 3 has all the new features from the original Second Life 3.0 viewer, such as mesh and avatar body physics, plus the following:
Everything that makes Dolphin Viewer 2 what it is, except for Qarl Fizz’ “Select Linden plants” patch
Marine Kelly’s RLV 2.7
Improved build tools (see this post for details)
Area Search (see this post for details)
Avatar and object derendering (see this post for details)
