Yes, it still exists and you can learn how to work the mode via a series of youtube videos by K8BZ, linked here: https://www.youtube.com/channel/UCFE00Ijq5WsDh7Y2Ak72CiA/videos?disable_polymer=1
We recommend “Outpost PPM” for a packet and board manager. Much of the set-up is also covered in the video series by K8BZ.
It should also be noted here that Packet Winlink (RMS) and P2P Packet Winlink (RMS) is also possible with through many of the TNCs and sound modems, and is just a matter of settings in most cases. An excellent encrypted and expeditious way to handle served agency sensitive communications!