What student doesn't like choices?
This TicTacToe board has nine extension activities based on all operation, number lines, and rounding that will extend students' content knowledge while they work independently. This works very as an independent project for early finishers or can be used in conjunction with stations. Activities included are designed to hit on many levels of Bloom's Taxonomy and encourage creative thinking.
I have used this in my classroom for students who need more structure than a math game, but enjoy showing their knowledge in creative ways. The activities also work really well in a small group where the group can actually decide what they want to do and complete the task together with you. The varied activities and structure allow all students to be successful.