I always liked the way emulation is handled on consoles (Nintendo's Virtual Console or Microsoft's OG Xbox and 360 emulators) best: emulated games are apps just like the native ones and are managed and started without additional launchers or front ends.
I wanted to have the same kind of experience on my other devices and I ended up making VCEverywhere (aka Virtual Console Everywhere).
In a nutshell, VCEverywhere is a framework for bundling a game rom, the corresponding system's emulator (supported systems are currently the same as RetriX) and some glue code to move input/output between host system and emulator (ok I lied: this what a front end does by definition - no way around it - but the experience is that of just installing/running a native game, with some basic niceties like save states or integer scaling). While the conversion process is as streamlined as I could make it, it still means using software development tools and is more involved than installing Retroarch and copying some files around.
Try the end result for yourself
Keybindings: WASD for arrows, OPKL for GBA's ABXY buttons and Enter for start - or a Playstation/Xbox gamepad connected via Bluetooth, tilde key or Left+Right triggers and start button to enter settings menu. Game does not support saves, so cloud syncing is disabled.
I have converted Butano Fighter, a homebrew GBA game that explicitly allows redistribution, to Windows (install using the same procedure as RetriX - certificate needs to be trusted and SmartScreen bypassed), macOS (follow these instructions since app is from unidentified developer) and Android (install like any other sideloladed apk) and uploaded it at the link above
For the time being I do not plan to release VCEverywhere publicly. I am posting this to understand whether there is interest in a solution like this, especially considering the learning curve involved.
If you are interested in VCEverywhere consider also registering your email address here in addition to replying.
Feedback, whether about VCEverywhere or the demo video (hopefully it's clear enough), is welcome.
Thanks in advance