A while back I installed a TV server program called Tvheadend using a PPA. The installation instructions and the program were on the site tvheadend.org which now appears to be dead (as of about three days ago, it seems). One of my pet peeves about installing software using apt is that you don't get a compressed installation file that you can hang onto for future use, like you would in Windows or MacOS. But what I was wondering is, does Ubuntu actually store the packages it downloads somewhere on the system, in a format where you could take that package and save it to an external drive or network share and then at some later time install it on a different system running Ubuntu, or even on the same system after doing a Ubuntu major version upgrade? I'd really like to be able to back this program up so that if I ever want to build another server I can still install it, but if there's a way to do that I am just not aware of it.
If there is not a way then that is really bad. I wish that Ubuntu would let you download some kind of install package to disk and then run that to install, as is the norm in Windows and MacOS, ESPECIALLY when you have to use a PPA to get software from a non-Ubuntu related site. But if there is a way, could someone please explain where Ubuntu stores those packages, and how I save a package for future use?
EDIT: The site finally came back up late Friday afternoon (US time) but thanks to those who replied!