Evolution invites you to construct simple stick creatures, then leave them to their own devices and let them learn how to walk. You can play it in your browser, but if you want to save your creations you'll need to download the desktop version (available for Windows and Mac).
Create joints, then link them with bones, then connect muscles to the bones. Once you think you have something worthy of the gift of life, select how many of the creatures should be in each generation, select an action (running, jumping, obstacle jump or climbing), then click Evolve.
At first, your poor creatures will probably collapse in an undignified heap, but the most successful member of each generation will be used to spawn the next, and after several iterations hopefully they’ll evolve into something capable of locomotion as they learn how to use their muscles to best effect.
My creature – a hideous tangle of muscle and bone – began by flailing and twitching like a stick man wrapped in a bungee cord, but eventually developed a kind of bouncy walk, using momentum from its horrible limbs to propel itself forward. Nothing as co-ordinated as actually walking, but satisfying nonetheless.
Download here: Evolution