Alternatives for XQuartz? XQuartz was always the goto for running X applications on a MacOS desktop. It's been a couple of years since the last version of Quartz and there is no activity on the github, so we may assume that the XQuartz project is dead.
Are there any alternatives for running X application on a MacOS desktop?
There are really no strictly better alternatives.
XQuartz is usually the best option for running an X server on a Mac.
If you're running older OS X versions, you might prefer X11.app from Apple.
If you're using older Mac hardware with PowerPC CPUs, you can also run XFree86 in the Darwin/PowerPC port (note that Xorg.org is originally a forked XFree86).
If you simply looking for alternatives - you could also take a look at WeirdX. It is old, it is slow and doesn't have as many features as Xorg - but it is an alternative:
http://www.jcraft.com/weirdx/
Besides that - there's always the option of running for example Linux in a virtual machine on your Mac, and then run your X server in there (for example Xorg).
Also you could look at alternative ways of connecting to your Linux desktop. For example you could use Xpra:
https://xpra.org
There's a macOS client - but there's also a HTML5 client for accessing the desktop through a browser.
Another alternative would be to use VNC instead of the X protocol.
UPDATE January 2021: An XQuartz 2.8 beta has just been released with support for Apple Silicon!