- AppImage. Basically the idea of "Apps" ripped straight out of MacOS and injected right into Linux. Works fine, but clutters your home directory with Another Folder and doesn't integrate with your desktop like a native package.
- Snap. Works on any system that can install snapd, is owned by Canonical (a pro or a con depending on who you ask), but also auto-updates and has occasional performance problems. Plus, snapd is generally kinda fussy.
- Flatpak. Sandboxing taken to it's (il)logical extremes. If you like random data loss, confusing package manifests, low-performance and generally broken software, this is the way to go. Of course, most people like it when their compositor doesn't break when installing third-party programs, so they avoid it like the plauge. It's a uniquely bad format, almost worth spinning up a Linux VM to try it for a laugh. Just make sure to use GNOME, it's useless anywhere else. That's the true hallmark of a cross-distro packaging solution!
So yeah, we're probably due in for Another Competing Standard. At this point though, I think most developers are contented to just ship an RPM and an Arch package and let everyone else figure stuff out for themselves. Honestly, I prefer that approach when compared to the blasted wasteland that is cross-distro package management.