App Pick: Outlook Mobile
Paul Thurrott's app pick of the week on Windows Weekly 504 is Outlook Mobile for Android and iOS. The iOS version in particular is the first to support a new add-ins capability, and the new feature will be coming soon to Android.
Outlook Mobile has already supported extensibility for quite some time for email accounts, calendar apps, and various storage services. The new add-ins capability applies to the email inbox, so you can have add-ins that appear when you're looking at email. For example, a transcription add-in would be able to show you the translated message within the app.