It all depends on the nature of your application. A video editor and a command line utility are so different!

Sounds like you already know the big players so I won't repeat them. Instead, here are some off-kilter ideas:

1. Casual use, general interest, notification-requiring, simple single-file data requirements, tolerant of desktop / mobile split sessions? Try making a chat bot for Telegram, FB, Discord, Slack..

2. Dynamic, visualization-focused UI with simple options that need to be tweaked interactively? Try Imgui[0] or Godot[1]

3. Scientific or data-centric stuff pulling in data from here and there, but meant for interactive exploration? Try Wolfram / Mathematica or an IPython notebook / GoogleColab

[0] https://github.com/ocornut/imgui/wiki/Software-using-dear-im...

[1] https://medium.com/swlh/what-makes-godot-engine-great-for-ad...