With yoongiUSB you can boot ISO files stored on a USB drive or USB hard disk without imaging them directly. You can put multiple files and it has some tools built-in. It's a fork of Ventoy.
At the moment it's not more than normal Ventoy but with a custom theme which is applied in the base image and not with the theme plugin. I'm planning to add more built-in tools which I find useful.
It will later also get a "real" source code. For now it's just the base image of Ventoy which I modified.