No you don't. You use the Messages app to send SMS/MMS to your Android friends.The Messages app sends iMessages, SMS & MMSUnless they have downloaded the iMessagesforAndroid app. And created an AppleID to use with it.
No.Your response seemed to indicate Fitbit app was proprietary and some/all others weren’t.Then according your definition above, Fitbit app is NOT proprietary because there are plenty of ways to get Fitbit data out of the app.Fitbit has created and support developer APIs to do just that! and they have done it pretty much from the beginning. That’s show Sync Solver gets Fitbit data to the Health app.