The video above shows a jailbreak tweak called Peekly. It’s a modification to the iOS lockscreen that adds weather, clocks, a calendar and more.
Reading the description gives a much more detailed idea of what the mod is capable of:
Peekly is a 2 page lockscreen theme for iOS. On the first page, you get the time and date. Currently you can choose between the default clock, a digital clock or no clock/date at all. More clocks coming soon! Dragging your lockscreen to the right will allow you to “Peek” at a 3 month calendar. This is the default peek. You can currently choose to put in a Twitter feed, yourGoogle Calendar events or an RSS feed. More options will be added soon. Swiping the lockscreen to the left will bring you to page 2, which has today’s weather. “Peeking” to the left on this page will show you a 4 day forecast.
features like these are the ones that make jailbreaking seem cool. The device may not do all the things you want it to, but slight modifications can make it much more enjoyable.