Within the next 24 hours, Microsoft will finally issue a major set of updates for the core “Metro” apps in Windows 8 and RT, in this case the communications apps. Here’s what’s changing in the Calendar app.

Note: I received a sneak peek of these changes late last week. However, I do not have the new app versions yet, and won’t until they’re publically released before early morning (Pacific Time) on Tuesday. (They could come as early as Monday night.)

This represents the third major “version” of the communications apps provided in Windows 8. The first version, of course, ships with Windows 8/RT as part of the core OS image. The second version was provided right before the general availability of Windows 8 and is installed alongside a ton of other app updates after you’ve booted into the system for the first time. You can read about the changes in that second update in Windows 8 App Update: Mail, Calendar, People and Messaging.

Here's what's new.

According to Microsoft, the updates to the Calendar app are aimed at keeping “all aspects of your personal and professional life organized.” In many ways, the improvements are more geared towards the “professional” end of the equation, however, since that’s what was lacking originally.

Here's what's new.

Find appointments more easily with updated visuals and improved readability. Calendar has gotten a subtle graphical update, making it look more streamlined and professional, especially for those with busy schedules. The big change is that the appointments are no longer big colored blocks.

See your work week at a glance. Microsoft has added a new view to Calendar: Work Week, which provides a Monday to Friday view of the week.

See current time in day and week views and when Calendar is snapped. In Day and Week views, and in Snapped mode, Calendar displays a time marker so you can see where you are in your day.

Check the availability of meeting attendees. As with Outlook, Mail now provides a scheduling assistant that checks the availability of meeting attendees so you can easily find a time that works for everyone.

Forward meeting invitations. Meeting requests are understood by the Mail app, allowing you to reply appropriately and directly from there. Forwarded meeting invitations retain the original invitation.

Send email to all meeting attendees. Exchange meeting requests are now automatically emailed to all attendees.

Choose more recurrence options. The current version of Calendar offers only a limited set of occurrence options, but the new version works more like Outlook, with far more options, including the ability to set an end date for a recurring event.