Imagine getting exercise and raising money for charity -- you can with the free app Charity Miles. When you download the app, you select a charity of your choice (like the World Wildlife Fund or Habitat for Humanity) and a corporate sponsor pledges money for every mile you work out. It's all synced to your smartphone, so you can't cheat your workout miles. All you do is hit start and then work out. When you're done, you hit stop, and the app tallies up your donation. Over time, your "sweat equity" can help do a lot of good.