The days you are free, taken from the calendars on your phone.
Tick the calendars that mean you are busy. Available works out which days are clear and writes the list, so a month with a fortnight gone in the middle of it comes out as “All except 6-17”.
Send it as text, as a PDF on your own letterhead, as a picture, as a calendar file, or as a link that shows the dates themselves.
Your diary stays on the phone. Your settings follow you to your other devices through your own iCloud.
Join the betaFree to test as a Beta version.