Ardour v6.0 has been released.
The developer says:
For some users, Ardour 6.0 will not look noticeably different from 5.12. However internally there have been huge engineering changes. Indeed, the primary reason for the very long interval between the two releases has been the scope and difficulty of these engineering designs and implementations. We are now confident 6.0 is a more reliable and usable program than any previous version of the program.
An extensive article describing what's new is available here.
The Source Code is free if you want to build it yourself. Purchase options for ready to run binaries start at $1.