RunKeeper, one of our favourite fitness-tracking apps for iPhone and Android, saw such uptake with their one-month freebie offer, they're going ahead and making their app, previously $13 in the App Store, free for everyone.
No word on how they'll make up for the revenue, though advertising or extra server-side features is always a safe bet. But being able to use all of RunKeeper Pro's advanced features without having to pay is a great thing, so more people can try it out and get into tracking their runs and goals. Recently added is an entry form for treadmill runs, which helps those in colder climates who still want to keep on track.
RunKeeper Pro is a (now) free download for iOS and Android.
Surpassed expectations and some news [RunKeeper Blog]