Very nice game! I'd buy the hell out of a longer version!
There's just one thing that misled me to thinking there was another ending. I'll try to say it without spoiling.
The word you are able to discover after finding the thing you get from beating the tic tac toe? I got it before beating the puzzle because I just couldn't find the logic behind it. Then I was able to finish the game without beating the tic tac toe, and the question mark at "Well Done?" made me think "well, there's a missing piece, maybe I need that for the true ending". Then I played again and when I eventually got the tic tac toe, I found out that the reward just helped finding the word I had already found.
By the way, I still didn't understand the logic behind the tic tac toe o.o