It's rare these days, but it happens: a (what I think) is a completely new UI element (or 'widget', in proper parlance).
In my quest for an Android Twitter client that doesn't suck, I stumbled upon Tweedle, a no-frills, properly designed Twitter client for Android that, as far as I can tell after a few days, does not suck. It integrates properly with Android and has an actual Android user interface - unlike other Android Twitter clients, it doesn't shove any non-standard UI crap in my face. Really, the complicated, overdesigned user interfaces many Android developers come up with just to show several snippets of text in a scrollable list (that's all Twitter is, folks) is remarkable. Let's save that rant for another day, however.
What I find most intriguing about Tweedle is that it includes a UI widget I've never seen before. Instead of a regular scrollbar, Tweedle has a vertical line that increases in length as you scroll down in your timeline, and decreases in length as you scroll upwards. If you reach the newest tweet, the bar disappears. It's a different take on the traditional scrollbar, but to me, it feels like a better fit for a timeline than a traditional scrollbar.
If you scroll far enough down, the line will reach all the way to the bottom. If you keep scrolling beyond that point, the line just stays there. A traditional scrollbar, like in, say, Tweetbot 3 for iOS 7, acts differently. Once the scrollblob hits the bottom of the screen, a new set of tweets loads, and the blob erratically jumps upwards, which is just plain weird when you think about it.
The traditional scrollbar - even a proportional one - does its job best when used with finite scrollable areas. Timelines on Twitter, Facebook, Google+, and so on, however, are essentially infinite lists, which causes traditional scrollbars to jump around whenever you reach the 'bottom' of your timeline and new content is loaded. The line in Tweedle does not have this issue, but it does introduce a new one - once the line fills up and hits the bottom, but you keep on scrolling - it stops conveying any new information.
Still, I find it a fascinating rethinking of the traditional scrollbar, and I hope to see it in more applications.