I’ve been playing a solitaire game known as Spider on and off for more than a decade. I was convinced it was not possible to win the game by any human means for a long time. In all the time, I had never come remotely close to winning, never getting more than one or two builds completed and removed from the tableau. This is worse than my luck with Pyramid solitaire which I had come maddening close in such cases where two cards in a reversed order would have meant a win. In the Pyramid case, it was trivial to prove to myself the game was winnable (and I eventually did win it). With Spider, however, it was not at all clear that a different arrangement of the cards would have made any difference.
Today, however, I finally won Spider. And I have a screen shot of the win to prove it. The screen shot is not doctored in any way. I will admit that I did use "undo" in a couple of cases but that is not relevant to the question of whether the game is winnable or not. An unwinnable game will remain unwinnable no matter how many moves a person takes back. So, for all you folks who are frustrated with the Spider game, it really is winnable.
The version I was playing is the AisleRiot version from Gnome. As far as I can see, it implements the rules correctly.