No, that's not an app that you see above. Although it may not look like what you were expecting, that's actually a screenshot of Twitter's mobile site on BlackBerry. Pretty cool right?
Twitter has had this HTML5 site up for a little bit but I found it interesting that not a lot of people know how well it actually works. Now, personally, I wouldn't replace the Twitter for BlackBerry app with the mobile site permanently as it still lacks certain functions of an app (notifications, shortcuts; etc), but if you're not a hardcore Twitter user and just feel like logging in once in a while, it's possible the mobile site may be your best bet.
The Twitter mobile site has a lot of the same functionality as the Twitter for BlackBerry app. The interface is extremely fluid and responsive and, depending on your data connection, it's pretty fast as well. Unfortunately it does lack certain features. For example, you can't see who's retweeted/followed you in the Connect tab, which I found really interesting since this is possible on the desktop site.
The Twitter mobile site on the PlayBook is in essence the same with the layout being slightly different to accommodate a larger screen. The same fluidity and smoothness applies and for someone that doesn't necessarily want to buy a Twitter client app on the PlayBook, the mobile site can be incredibly useful.
I'm very happy that Twitter has made this mobile site available as it brings another alternative for mobile users of any platform to use their services. HTML5 is here and it's here to stay for quite some time. We're lucky that our devices are great and our future BB10 devices are going to be amazing at rendering HTML5 content. That's a huge plus for BlackBerry and something we ought to be proud of. Not everyone can say the same.