SolveMe Mobiles

The puzzles at SolveMe Mobiles are linear equations disguised as perfectly balanced mobiles. The early puzzles are simple while the later ones require solving systems of equations. The interface is elegant. Drag a beam to have the corresponding equation appear. Drag a shape that's on both sides of an equation to subtract it. Drag a common factor to divide by it. Substitute by dragging a shape that you've isolated on one side of an equation to somewhere else it appears. Create your own mobiles. Play without creating an account or create an account to save your progress and creations. (No email is required to create an account, though those over 13 may include an email for the purposes of password reset.)

WolframAlpha

Type in, for example, an equation you want to solve, a function you want to graph or the names of two cities. You will want to keep playing. This video by Robert Talbert gives some ideas about how a math teacher or student might begin exploring.

Solving Linear Equations with Step-by-Step Checking

This is a very slick applet from WisWeb for providing practice solving linear equations (and showing your work!). You can use one of the 20 equations given or type in one of your own. Specify what you want to do to each side as the next step (e.g., add 4, combine like terms, distribute) and then do it. The applet will then indicate whether you have correctly carried out the operation you specified. Continue until the equation is solved.

There are a couple of other versions of this applet which have more practice problems, grouped by difficulty, but they do not include the option to enter your own equation. You can find them here and here.