It is a gecko engine propelled xulrunner. A quick look at the source code will tell you it is extensible just like other gecko-engined apps. Mr Glazman already conceived one Diavolo extension for his blazing new editor.
So we can expect one day to host some extensions to translate for this exciting new bird. 🙂
The logo is quite impressive, no doubt web designers will grab code fiercely with BlueGriffon claws!