If I purchase just one adobe app do I get to use that app in other computers?

And individual license is the same no matter which plan you buy -- All Apps or Single App. 

• The subscriber is the only person who can use it.
• You may activate on up to 2 devices (home/work, desktop/laptop) but you may use only one device at a time. 

Make sense?

For environments with multiple users, Adobe offers licenses for Teams & Enterprises.

https://www.adobe.com/creativecloud/business/teams.html

Cloud License allows 2 activations at a time http://www.adobe.com/legal/licenses-terms.html
-Install on a 2nd computer https://community.adobe.com/t5/Get-Started/Installing-creative-cloud-on-two-devices/td-p/6048133
-https://helpx.adobe.com/creative-cloud/help/sign-in-out-activate-apps.html
-Windows or Mac does not matter... 2 on the same operating system, or 1 on each