Hi!
I found MultiOS-USB is added into sparky.
However, there is another multi-os-bootloader called ventoy:
https://www.ventoy.net/
https://github.com/ventoy/Ventoy/
MultiOS-USB is started at 2020-01, and ventoy is started at 2020-03
Which one is better?
Sparky (rolling) Works with Ventoy
I've got several usb sticks with ventoy installed on them and multiple Linux ISO's, most work the others I keep and burn to another stick with Etcher as and when I need them.
But yes ventoy is very good.