Best approach to a simple app.

My Daughter is at College . They have a shop they run there for 2 hours a day.
She wants some way that people can see if the shop is open online (ok, easy simple xojo web app), but also a way for people who want a notification to be notified via their ios/android device, ie shop closes in 15 minutes.

Not sure if there is a free /opene source way to do this, else I thought XOJO web, the person opening the shop and log in and say open.
People could set up logins to update their settings about if they want alerts or not.
Is there an easy way to send alerts to IOS devices? (maybe up to 100 messages a day max I think)
Thanks for any thoughts before we embark on this…
I can provide an old computer for it to run on. Have far too many of those :slight_smile: