I was using Parallels Desktop and suddenly it has crashed with "Parallels Desktop quit unexpectedly" error message.
Changes released in macOS 10.14.4 update. Apple is aware of this issue and is preparing a fix for the next build.
Check the macOS version you are currently using:
1) Click on Apple logo in the left top and select "About this Mac"
2) If the version is 10.14.4 follow this list of instructions.
3) In case you have a backup of one of the previous macOS versions (10.14.3 is more preferable) rollback to it until macOS 10.14.5 is officially released. This article or Apple support technicians can help you with it.
4) If it's OK for you to test beta versions of macOS you can upgrade to macOS 10.14.5 as this issue is fixed there.
In case the macOS version you are using differs from 10.14.4, please contact Parallels support.
NOTE: In case you are using Parallels Desktop 12, update it to the latest build by downloading the installation image from here.