Free with Office 365 / Microsoft account. Decent desktop & mobile apps too and integration into Outlook/Teams. API available via the Microsoft Graph and integration with PowerAutomate if you want IFTTT/Zapier-like functionality.
All multi-device/synced TODO lists have authentication to keep it private. That's half the utility. Add an item when on your laptop or iPad then when you need it outside you pull out your phone.
TickTick also has markdown notes and a calendar. I use the notes probably as much as lists, which fit desktop usecase better. Lists could be fine if it was mobile only but still annoying.
I highly doubt that. It's just they are the type of apps no one knows about because a developer will throw a TODO app together over a weekend then not support, market it, or abandon the server after a couple years. As I personally experienced at least twice over the years.
If you ask GPT they recommend these that fit the criteria (among quite a few others):
- https://2doli.st/ follows the same principles. but as I said before, state in the URL does not work for me. Every update changes the URL.
- https://moartodo.com/ is local. Can't be shared.
- https://flask.io/ I like it. That's the spirit.
If it does that's recent, I used it for ages before creating an account. I did a while ago, for some features that needed it (a joint list with my wife, mainly) but it wasn't mandatory, and still free.