[aardvark179]

Just the normal iOS notes app.

[therealdrag0]

For checklists, iOS Reminders app is great,

[loloquwowndueo]

But you can’t share it with people running Android.

[8n4vidtmkvmk]

Microsoft Todo, formerly Wunderlist, may or may not have an iOS app. It's pretty good.

[loloquwowndueo]

Todoist exists but both require a more complicated setup.

It’s been established the main point of the posted app is having shared lists with no install or account creation required, just share a link.