Does not do anything else it seems. Cost nothing maybe, but time is money. You may not want to spend time learning a tool that'll only do Bootstrap. Unless perhaps if you plan on doing JUST Bootstrap.
The interface is divided into sections: a dashboard with account settings, a panel with blocks and the canvas. It's easy to drag and drop website blocks and edit them with parameters. There is a simple to use text editor.
Those who are new to editing will find the instructions on the BuildBootstrap page easy to understand and follow. The information presented is concise and is displayed neatly in one page.