Basically no one uses /var/tmp for anything (and nobody should either). World writable directories are a mistake and only continue to exist because apps assume they are available.

/tmp and friends are poorly named. They really should be /shared or /dmz or /freeforall or something.

* If you need service-specific tmp space use RuntimeDirectory or PrivateTmp if your app is hardcoded to /tmp.

* If you need service-specific persistent data that goes in /var/lib/your-app.

* If you need temp space for your user it's at /var/run/user/your-uid.

* If you need more than one user/service to share files but not everyone then god have mercy on your soul because all options are bad. There sure are a lot of them but none of them are at all satisfying.