One of the new features that was much awaited was the new Joomla Router, offering improved URL's. This would give some nice improvements in how URL's in Joomla will be created (see my earlier blogpost about this). Unfortunately though, this featured has been pulled from 3.7.
I will not spend a lot of words on this, as the full details of this decision have been published on Joomla.org: https://developer.joomla.org/news/674-statement-about-the-new-router-feature-for-3-7-0.html. In short, it appeared there were too many issues to release the feauture in the wild.
The aim is to move the new router to Joomla 3.8. However, this will require a lot of work. The 3.7 router still depended on existing router code and to function correctly, the code probably needs to be fully re-written. Also, the developers will look at Joomla 4: users should be able to upgrade without broken URL's.
In the mean time, Hannes Papenberg, who wrote much of the 3.7 code, might release the 3.7 code as a separate plugin for users that would still like to use it: