The early dropControllers were part of the larger project I called camControl. This was a multi-trigger device similar to others you have mentioned.
When the dropController part of the project became fairly large I separated it and it became a dedicated drop device.
Adding a trigger to the dropController is possible and if all you want is a simple single trigger input it would work fine. However, if you want more complex triggers and better control there are better solutions than modifying the dropController. Have a look at the cameraxe and Michael Ross’s High Speed Photo Trigger.
If you want to get ideas for the electronics, take a look at the Hiviz website. Lots if useful stuff there.