Pneumatic die grinder or electric rotary tool
Pneumatic may be lighter weight, but you need a compressor that can keep up with it, and the exhaust airmay be a good or bad thing depending on what you're doing. On the other hand, compressors have other uses too.

A third option would be a flex-shaft tool.

Before buying any of them, know what you're going to do with it. Unless you have a specific task you need it for, you might be better advised to invest in a completely different kind of tool.