As of yet, no one has answered the question correctly. What was the first third-party game for the 5200? I am getting worried. Perhaps I am wrong...
The answers that I have received are: Frogger (one person) and Q-Bert (three people). If I am wrong, and one of those is correct, someone with some authority needs to tell me.
In case anyone is wondering where I got my information, I read it in a newsletter within the last year.
If one of the above answers is right, the prizes, 5200 Qix and Star Raiders, will go to the first (and, if relevant, second) person who answered the question correctly. Since I am not perfect, I apologize if I am wrong. In the future, I will make sure any contest answers have absolute, concrete proof!