On Ubuntu 16.04 and a program I'm trying to install downloaded a bunch of 'par2' files. Archive manager doesn't seem to recognize them. What application should I use to open these?
par and par2 files were more common in the days when Usenet was a little more popular and the parchive was intended to increase the reliability of transferring files via newsgroups.
Under Xenial Xerus you can use these files with
sudo apt-get install pypar2
This give a basic gui from which to manipulate the files: