You never need to know any of this to use Caliu. But if you are curious about what happens behind the screen, this section explains it in plain words, naming the real technologies along the way.
The whole system in one picture
Caliu has three kinds of pieces:
- Your devices. Every app (web, iPhone, iPad, Mac, Apple Watch, and Android) keeps a complete copy of your notes in a database on the device itself. This copy is the one you read and write.
- Caliu's server. A small service running on Cloudflare's network. It keeps a copy of your notes and passes changes from one device to the others.
- Everything you connect. Share links, the public API, and AI tools connected through MCP all talk to the same server, through the same doors as the apps.
When you type, your device saves the change on the spot. A moment later, in the background, it sends the change to the server, and your other devices pick it up the next time they sync.
The copy on your device comes first
Most cloud apps work the other way around: the server holds your notes and your device borrows them for a while. Caliu is local-first. The copy on your device is the primary one, and the server is a relay and a backup.
That one choice explains most of how Caliu behaves:
- It opens instantly, because nothing has to load from the internet.
- It works fully offline, because there is nothing to wait for.
- Your notes never depend on a server staying online. If Caliu's servers disappeared tomorrow, every note would still be on your devices, ready to export.
Why it is built this way
Caliu is made by one person. That rules out complexity for its own sake and favours a few simple, solid pieces that each do one job. It also explains two other choices you will read about in this section: Caliu runs its own sync instead of iCloud, so your notes are not tied to one brand of hardware, and every app is native to its platform, so writing feels at home wherever you are.
In this section
- Where your notes live: the databases on your devices and on the server.
- Inside sync: how changes travel between devices without getting lost.
- The server: what runs in the cloud and what it does.
- Native apps, not a wrapper: how each app is built.
- The editors: how each app turns Markdown into the page you write on.