Where to install software that is not in the repository?

[Mishimainizu]

Until now I only installed packages from the official repository. But what about other apps that comes as tar files? Where is the best location to install them?

[skidoo]

https://wiki.debian.org/FilesystemHierarchyStandard
Ultimately, it's your choice, but the convention has been to place 'em in /usr/local/ or /usr/local/bin/

[mxer]

I usually keep that type of program in my home directory, so that they can't interfere with the system.

In the old days, they'd likely go into /opt, but, /usr/local/bin would be a reasonable choice.