If you're one of the people that actually uses Microsoft's Calendar app that's built into Windows 10, you're in for some good news. According to Aggiornamenti Lumia, the app is getting a big redesign. Moreover, you should be able to test it out pretty soon by turning on app previews.
You can see at the top that there's extra space to see a new landscape theme. Apparently, that's the only theme available at this time, although the report does suggest that more will arrive at some point. There's also a new hamburger menu on the left, which looks like it does similar things as the existing hamburger menu, although there are new Outlook and Exchange icons below it.
As you can see from the image above, there's a new window for creating events, rather than it taking up the whole app window. The report says that settings is getting an overhaul as well, in terms of layout and features, but it didn't go into further details or show a screenshot.
It's unclear when the new app will arrive, although we'll probably see it in a Windows 10 Insider Preview sooner rather than later. At some point, you'll be able to turn on app previews from within the Calendar app.