Ultralight dev here-- most work has gone into porting Ultralight to various platforms (game consoles and ARM64) the past 2 years. The main focus is less to replace Electron and more to get modern HTML/JS/CSS running everywhere.
The desktop layer (AppCore) is indeed missing some support but I have some cycles allotted to finish them in the next dev branch (1.4).
The desktop layer (AppCore) is indeed missing some support but I have some cycles allotted to finish them in the next dev branch (1.4).