Not sure if this is the right forum for this, so please move it if it seems more suitable elsewhere.

I am about to start work on a number of modules for a community XOOPS site.
These modules will be designed to work together or by themselves.
For example:
One module can store contact details for people, while another stores information on organisations. When both are installed, and some preference enabled, it wil be possible to list the contacts for an organisation and vice versa.

Has anyone done anything like this before and is there any standard way of doing this?

Ideally I'd be looking at some form of plugin system, so that if there is a preffered contact module a plugin could be written to link the organisation to contacts from that module instead, for instance.