I wrote recently about the paucity of 3rd-party add-ins for Enterprise Guide. I finished the post by wondering aloud whether there were more that I hadn't found. Well, I've had no reports of any 3rd-party add-ins, but in Chris Hemedinger's SAS Dummy blog he summarised a good range of SAS-supplied add-ins that are available for free download.
Whilst they are largely unsupported, they certainly provide some jolly useful functionality. And the source code is provided so you can support them yourself.