From FarmShare

To obtain a list of installed software from the command-line on machines running Debian or Ubuntu:

dpkg --get-selections

Use grep to search for specific packages or groups of packages:

dpkg --get-selections | grep r-cran

If a package is missing but available from the standard Ubuntu repository you can request installation by submitting a HelpSU ticket. You can look up information about packages at http://packages.ubuntu.com