This is not
Messiah:Animate has this feature called "Animate Immediate", wich works pretty much like the "Tweak Mode" in Wings3d, except with bones instead of vertices/edges/faces.
Check out the GIF animation here
(5. Animate Immediate
It works as follows:
If you hover your mouse pointer over a bone, it gets highlighted (pre-selected), and if you drag the highlighted bone, it automatically get's selected and rotated.
Simply release the mouse button to finish, very fast and simple.
(With blender's RMB+drag you have to click an additional time to finish, and you don't get an indication wich bone is about to be selected, it's much slower)
This was suggested in the Wiki by someone else already, but the comment on the request suggests that it wasn't clear exactly what the request was.
For reasons of mouse strain and accuracy I am not convinced this 'tweak' is better than what we offer. A RMB click followed with LMB assign is very friendly to use, not to mention that you might want to constrain rotations or translations inbetween.
Further doing pre-hilighting on mouse-over is neurotic & lazy coding. A click-select should just always hit the right bone (object, vertex, etc). If not, then we have to code it better
Sorry but I think the Animate "Inmediate mode" is far better too.
This feature is already in Tuhopuu (works really nice) and whould be nice if is aproved to insert in Blender
May be if you don't like it, we can have it by an option in User Preferences?
"Some Day, All Will Be Digital"