A simple example of an utility application is log. To use it in your application you can write:

use('log', '0.1');

...

log.debug('Your log message');

The first line includes the file http://www.akshell.com/apps/log/code/0.1/__init__.js which is an interface of log. Then you can view your logs at http://log.akshell.com/

The admin of log maintains consistency of the interface; so other developers can use it.

Anybody can use your app if he trusts you. If you don't maintain consistency of your utility interface, nobody will use it.

It is not like friending. The friending itself can be implemented as an application.