MatterControl, like most everything in the real world, fall under many licenses. The code in GitHub is under the license it states (typically BSD). Some of the plugins are copy write MatterHackers. The name 'MatterControl' is a TradMark of MatterHackers. Basically, depending on what you want to do, it can be complicated.
If you want to get the source and build it or contribute a fix, or you want to build a new feature that you run your self, absolutely. If you want to distribute a new piece of software and call it MatterControl, that is not a permission in the license.
The simple answer is, you can probably do whatever it is you want within the license as is. The goal is MatterControl is open source software and the complexity is only in the places where there are other considerations, like marketing or user security.