Delve the Dice Game is a free Yahtzee-like fantasy game developed by Drew Chamberlain. I used this as a basis for a Strike Witches variant, with 5 missions. It can be downloaded here (zipped, Word documents, some PDF's). It may still need a few tweaks, but it's still pretty fun to play. Just need a lot of 6-sided dice.
Here's a photo of Mission 1: