I'm in the process of installing Ubuntu linux on my old PC tower (I'm building a trusty audio workhorse). But I forgot the name of the web site which carries the latest Debian packages that aren't in the Ubuntu repositories.
It's called getdeb.net, all the latest, freshest, lovely software. The proviso is (there is always a proviso) that the software won't be supported by Ubuntu.
Addendum:. Thanks to fancollo for his comment, pointing out an alternative site called Appnr.com, which is a similar site but slicker and you can install packages directly from the web site.