Speaking to your computer hasn't quite caught in the way 1970s science-fiction suggested it would, but it is possible. If you want to talk to your computer to launch apps, TUAW shows off how to do it in OS X Mavericks.
TUAW uses an automator script and the new "Speakable Items" option in Mavericks (System Preferences > Accessibility > Speakable Items) to launch apps. When it's set up, you simply hit a key on your keyboard, speak a phrase, and that launches the apps you choose. Their example is a simple "Good morning" to start your day, but we're sure there are all kind of clever uses for it. Head over to TUAW for the full video tutorial to set it up for yourself.