This is an extension I created as a basic extension object template. Hopefully, it is a helpful starting point in creating new extensions and can be copied and pasted, then modified to get the ball rolling.
I created this along with my Extension Object Basics documentation in the hopes of giving developers a good starting place for the basics of object extensions.
If there are any updates or other changes that you think I should make, please let me know and I can add them.
I've updated this post to now be a zip file of two templates. The one named template.qar is a template I built more with the intention of showing all of the most common properties and settings, including select boxes, check boxes, etc. The one named template_simple.qar is a bare bones extensions template that may prove to be more useful as a base for copying and pasting to create a new extension. In both of the templates, I've also improved the select dropdown property support.