> except for one: It was closed source.
Two, it was not responsive. It was written for fixed sizes with keyboards and mice. Not portrait displays with touch screens, nor AR/VR displays with pointers/hands, and for resolutions of the day, not reflowing / resizing to fit the user's device
Responsiveness is overrated. I use a phone with one hand (unless typing). I use a tablet with two hands (unless on a stand), and I use my PC with a mouse and keyboard. The biggest benefits for me is when the developer think about the layout and specific widgets for each type of device and not merely reflow them.
Something like procreate would be horrible with mouse/keyboard. UX is not merely a function of size.
Flash generated SVGs so it could be resized to any screen.