I wrote a Chimera extension that allows moving just selected atoms with the mouse. This is for modifying molecular structures. Here is the code http://www.cgl.ucsf.edu/home/goddard/temp/moveselection.tar that adds mouse modes to move selected atoms. The archive contains a directory called MoveSelection. Put it in your Chimera distribution in chimera/share or on Mac in Chimera.app/Contents/Resources/share Then when you start Chimera use menu entry Favorites / Preferences, and choose category "Mouse" from the preferences dialog. This shows the mouse modes table with the available modes along the top line. The last two are for shifting and rotating selected atoms. Reassign mouse buttons (say buttons 1 and 2) to these modes and you can move selected atoms. There is no undo. I'll have to make this easier to use and put it into Chimera. Tom