What is the difference between droid Motorola and droid HTC?

So the "droid" phones are running an operating system called android.

Both the Motorola Droid and the HTC Droid Incredible (I assume you are talking about these two) run android.

The difference (aside from physical features) is that HTC has added another interface on top of the regular android called "HTC Sense". It is still running android it just has extra features, widgets, and different styled menus than the original android system.

The Moto Droid runs just android for the most part. There are some tweaks that Motorola did but thing too crazy. The Droid 2, X, and Pro all have a "NinjaBlur" interface.