I've been working on an open source layout editor for use with AGEMAME. Currently, its not a simple task to build a layout for AGEMAME, so I decided to try and help the project by creating a layout edtior to simplify the task.
You can find details of this here

including the binary release done just today of a very alpha version of the editor.
It's still early days though, and I expect there to be some tough times ahead...