This is a review game I play with my classes during our Linear Equations Unit - they love the fierce competition and the speed of the game.
The PowerPoint is 12 slides, each slide with a system of equations. Students are challenged to determine if the lines are parallel, perpendicular, or neithre (intersecting) as quickly as possible. I arrange my desks in rows, and I have the student at the end of the row select one of the three cards (PARALLEL, PERPENDICULAR, or NEITHER) and pass it to the student in front of him/her. The chain continues until the card gets to the student at the front of the row. Fastest team (with the correct answer, of course) wins. The PPT has animations with the correct answer for each system.