Motorola has broken off part of their core build system, known as MOTODEV Studio for Android, and merged it into the Android Open Source Project. Previously, the closed-source Motorola tools were an alternative to a standard Eclipse IDE setup, which allowed key features like easy localization, drag and drop of shared code snippets, and browsing and manipulation of SQL databases through Motorola's tool.
With the new merging of the core plugins to the AOSP, developers can now build and use the tools through Eclipse, which is by far the most popular IDE for Android development. Motorola has full instructions for getting the code via GIT, building it, and integrating the plugins into an Eclipse workspace. See the source links below.
Confused yet? That's OK, this is pretty nerdy stuff. Here's the layman's version. Motorola used to make a stand alone set of tools that developers could use to make apps. A couple people I've talked to said they were pretty nice tools, but the majority of folks felt it wasn't worth losing the integration of Eclipse -- which is the program most folks use to write and build Android apps.
Today we learn that Motorola has open sourced a good number of these tools, and merged them in with the rest of the open source tools and code of the AOSP. Now developers can use Eclipse, but still download and build the Motorola tools as plugins for Eclipse itself. More and better tools mean more and better apps. We all like more and better apps.