Twitter has spawned many products and services—many of which aren’t terribly useful, original, or even functional. Put Tweetdeck in the “useful” camp—so much so that Twitter bought it.
Open APIs and free SDKs let developers take platforms in interesting directions. From there, developers form ecosystems. They create new products and services. That is, they externalize innovation. Rinse. Cycle. Repeat.
Once you get your mind around this, you truly understand the power of the platform.