Apple has released the third beta of the next maintenance build of MacOS Mojave, build 10.14.3. The update was released earlier today to the developer community but now has been released to the Apple Beta Program members as well. If you are part of the beta program, you should the update available on your Mac via Settings>Software Update. The new build is 18D38a for those keeping score at home.
The third beta comes nearly three weeks after the second beta, which was released December 19, 2018. That is slightly longer than the normal one-to-two week cycle between beat builds but there were two holidays in the middle of that swing, Christmas and New Year.
As for what to expect with this build of MacOS Mojave once it is released to the public is… not much. This is very much a maintenance build that will mostly be focused on bug fixes and other performance improvements. There will be virtually no new features in this build other than some potential minor cosmetic updates. All that said, Apple has been down to throw in a late feature but given we are likely halfway through the beta cycle for 10.14.3, it is unlikely at this point.
As to when the public will see this build, that is not clear. Apple never publishes release dates but based on other similar releases in the past, we likely will see it towards the end of January or early February.
Finally, Average Apple Guy does not recommend running beta versions of MacOS on your production Macs. You could run into a show stopping bug that causes you issues.