very rough around the edges, and the ui leaves a lot to be desired, but it's extremely powerful, and a much more solid alternative to substance designer than, for example, texturelab
In 0.92, space bar on the workspace shows a menu to create nodes. You can move all side panes around or hide them using the View->Panes menu.
If you want to test (and give feedback on) the upcoming 0.93 release, you may want to grab a development build there (just click the most recent action): https://github.com/RodZill4/material-maker/actions