If you read that title and envisioned a cutting-edged, highly polished dolphin simulator, I'm sorry to be the bearer of bad news. For everyone else, Dolphin Emulator, free software that allows users to emulate copies of Wii and GameCube games, is now on Steam, where it will presumably continue to be free. The fact that they haven't been smacked with a cease and desist by the notoriously litigious Nintendo is baffling, but the Steam page is very careful to tiptoe around anything that may bring the hammer down. For instance, they don't actually name Nintendo or the consoles they emulate, and make it very, very clear that you should have completely legitimate legal digital copies of the games you use the software with.
If you've ever wanted to replay Super Mario Sunshine but sold your GameCube years ago, this may just be your chance… as long as you do it legally, of course.