The app allows you to set reminders, make to-do lists, and set timers or alarms.
Microsoft seems to be moving Cortana out of the default Windows platform by releasing a dedicated app.
The Cortana beta app is currently listed on the Windows Store. As the description indicates, the app allows you to set reminders, make to-do lists, and set timers or alarms. It can also answer your questions.
It is unclear why Microsoft is removing the smart digital assistant out of its Windows built-in form. However, by doing so, Cortana may receive swifter updates than through combined ones with the Windows platform.