Rating:
5/5 all essential functionality available offline by default, works reliably
4/5 most key functionality available offline by default, mostly works
3/5 some functionality available, may require configuration or manual faff
2/5 minimally functional when offline, considerable configuration or manual faff required
1/5 barely functional offline, complex configuration or effort required to use
0/5 not functional without an Internet connection

Principles:

- Computers should manage state not humans
- No fuss: no complex configuration

Pocket - 5/5 on iOS
Syncs everything for offline reading in background, all actions (e.g. archiving an article) are stored for
later run on connection.

Instapaper - 5/5 on iOS
Syncs everything for offline reading in background, all actions (e.g. archiving an article) are stored for
later run on connection.

Evernote - 4/5 on iOS
Needs a premium subscription to use offline. Requires you to choose whether particular notebooks are
downloaded for offline use.

Things - 5/5 on iOS
Syncs when there is connectivity. Otherwise can be used fully offline.

1Password - 5/5 on iOS
Syncs via Dropbox or iCloud when online. Can be used fully offline.

Fastmail - 0/5 on iOS
No ability to use offline.

Weather - 0/5 on iOS
No ability to use offline.