It’s the one part of the MS Office family that I could really use occasionally, but not to the extent that I can afford to buy it. Will LibreOffice ever extend to cover this, or is there already a recommended Open Source app that is compatible with MS Publisher files?
From LO version 4 a .pub MS Publisher file will open in LO Draw. Draw is the nearest equivalent to Publisher in the LO suite. You cannot however save a Draw file as a .pub file. There is an open source program Scribus which can open Publisher files.
In the open-source world there is Scribus (https://www.scribus.net) for desktop publishing. It is available for Linux, OSX and Windows.