Algebra Tutor for Android phones is an amazing, free app that is not just for practice. There are short lessons with guided practice and solutions with all steps worked out covering: Linear Equations, Polynomials, Quadratics and Scientific Notation. This is perfect for students that need a little bit of extra help or, parents who panic when their kids ask for help.
The practice section has a longer list of topics to choose from including fractions and variable expressions. The practice section has workspace and, like the "learn" section, you can choose to see the steps worked out.