I have used The Game Crafter to publish the two games I have created.  My first game, Make an Offer, was created as an experiment in order to understand the process involved in creating a game.  Although addition of large numbers is involved, the game wasn't created to be a math game for the classroom.  The second game, Solve and Settle, was created specifically to be used in the math classroom and requires students to solve simple algebraic equations.  Click the picture for more information about each game.
Make and Offer

Solve and Settle
A two person card game of property acquisition where each player must offer an amount for a property greater than their opponent.

This was the first game that I created.  It isn't a math game for the classroom, rather It was created in order to understand the game design process.
A two to four person game where players play the roles of settlers of a new territory.  In order to settle the territories players must solve algebraic equations.  The person (or team) that settles the most territories rules the land.

A math class specific card game.  This game is designed in order for students to practice solving algebraic equations.