Developing for is was a fun challenge. I had a device that had 4MB of memory total. This was RAM, Data, and application space. I created an "app" that had plugins. When you ran the HotSync is asked which plugins you wanted to "install", then based on which ones were installed it copied over the data you needed.
I loved the documentation. It might be the only SDK documentation I read with joy. It just clicked with me.
Gremlins. I liked this program as well. I don't recall if it was a simulator only or if it ran across on device. You could tell it to just wreck havoc on your app. I would set it up to run over the evening or weekend and I would just fix any bugs that occurred during that time. It would click every button, add weird text to all input boxes, just smash everything. It found many issues for me. When I came back over the weekend and there were no issues, I shipped my app. I still had users running it up until 2010.