The HTC Butterfly features the usual set of organizer applications. Office document viewing is done through the preloaded Polaris Office app. It supports Excel, Word, PowerPoint and more and lets you view and edit files on the go.
The calendar has four different types of view: daily, monthly, agenda and invitation. Adding a new event is quite straightforward and you can also set an alarm to serve as a reminder.
The Agenda view shows a list of all the calendar entries from the recent past to the near future. Invitation view only lists events with invitation info attached to them. The day view also shows the weather forecast at the top of the screen, which is a nice touch.
Naturally, the Calendar supports multiple online calendars (including Facebook), only one of which you can sync with your computer. You can also easily show/hide the ones you don't want.
There is also a calculator on board. It is nicely touch optimized with big, easy to hit buttons. Flipping it horizontally enables some more advanced functions like logarithms.
The World clock (also part of the Clock app) is like a mini Google Earth - it shows a 3D globe and you can rotate and zoom in on it freely. You can add cities that are pinned to the globe (and also visible as a list below it).
The HTC Butterfly features an alarm clock application, which can handle multiple alarms, each with its own start and repeat time. You also get a stopwatch and a timer in the same app.
HTC Note app is also onboard. It is somewhat similar to Samsung's SPen - you can take various notes, add drawings, pictures and dictations. Sharing and printing options are also available.
There is HTC Tasks app as well. It does exactly what the name suggests and can access your Google Tasks. There is no location-based reminder support unlike with Any.DO, iOS's Reminders, etc.
Another HTC exclusive app you get is a very basic Movie Editor, which can be used for trimming videos among other things. Flashlight has seen a slight revamp in the UI, but provides the same basic functionality. It still allows three levels of brightness.
There's a voice recorder on the HTC Butterfly too. It's a pretty straightforward app with a nice interface.
HTC's Weather app is here too. It became popular years ago with its cool weather animations and widget. You can preset many cities across the globe and it uses the Yahoo! Weather info (much like Samsung and Apple do).