The Transition to Algebra (TTA) project, an initiative of the Learning and Teaching Division at Education Development Center, Inc. (EDC) includes a wonderful collection of Mobile Puzzles. Visit solveme.edc.org to play SolveMe Mobiles (also available for the iPad.) Further details are in this post: Mobile Puzzles Algebra.
Looking at the menu, you will see categories with different levels of difficulty available from very simple puzzles to rather more complex puzzles which promote good mathematical thinking.
Students must determine the weight of each object shown which makes a good introduction to the skills required to solve equations, linear and simultaneous.
Diamond Collector (NRICH game)
Can you enter the equations of 3 lines to collect as many diamonds as you can?
On Math Playground:
Tim Brzezinski’s GeoGebra resource is great for some hard thinking on expanding brackets. Not only do students get to practise this skill we have the added thinking needed to make sure each digit is used once only. The activity encourages what if type questions, what can we put outside the brackets? Are there some numbers we can’t put outside the brackets? Doing this on GeoGebra is great, it’s easy to drag the numbers around and the resource will check any proposed solution.