Hi Ki,
You can simply copy app(s) folder and paste to another installation /egroupware root folder where the other apps folder are. After copying, then you need to go to setup->manage applications, and install the app(s) from there.
Although, you need to be concerned about couple of things before taking this action, like if both source and destination installation are same egroupware version (For instance, copying app from Trunk version to 1.8) which might cause breaking the whole system. And also, it is recommended to make backup of your destination installation before installing new apps.
Best regards,
Hadi
