WikiName for Together platform, a UML tool that competes with RationalRose, only with real round-trip capability. You can literally edit text in one pane (or even in your favorite external editor or IDE -- being certain to save changes), and instantly see the change to your UML diagram in the other pane.
TogetherSoft tool for Java/C++/IDL from PeterCoad.
Other mentions here include:
See also (and perhaps refactor together): TogetherJtool
There is also a TogetherSolo, TogetherEnterprise and TogetherControlCenter.