Very simple but incredibly (IMHO) useful script for people like me who run multiple instances of 3ds Max and want a copy / paste type of workflow to move geometry back and forth. Personally I use it to copy an object out of a huge production file and paste into an empty Max file for detail work...
There's no UI - you just assign it to shortcut keys.
http://www.scriptspot.com/3ds-max/scripts/copy-and-paste-objects