Solve Me Mobile allows students to develop algebraic thinking through balance puzzles like the one below. The site offers a collection of puzzles and allows teachers (or students) to create their own.  Students can write on the screen to work through their reasoning if they want. The site also gives gentle feedback letting students know if the puzzle is completed or not by showing if the scale is balanced based on students’ answers.

Students can set up free accounts. They don’t need to in order to solve the puzzles, but with a free account, they can save their progress.