This probably isn't cool, popular, or what you want to hear. But for client-side software, use the native GUI library for each platform. Write the core in C or

This probably isn't cool, popular, or what you want to hear. But for client-side software, use the native GUI library for each platform. Write the core in C or C++. Abracadabra. It's cross platform, no issues, no bloat, no extra fees. With experience it can be fast to develop too.