Mika, the Alibre API allows production of Add-ons which can be linked to a button on the Add-ons ribbon or even have their own ribbon tab. You can find a few examples in the API section of forum.
Script uses the API, but is meant to be simpler to use/get started for those not having as much development experience - so scripts will typically be a little clunkier to launch, but you'll get access to things that may never be created as a full add-on. Alternatively, script might give a way to test out an idea, before putting in all the effort to produce an add-on.