jstash

For static sites, prototypes, scripts and cron jobs that need JSON at a URL, jstash offers JSON Bins. For apps that need private per-user data without a backend, jstash Apps use the login your app already has.

Free, no card: 100 bins, 1 app with up to 100 users. Pro: US$5 a month, billed monthly, cancel any time, adds private bins (only your API key can read them), 1 MB per bin or document and 3 apps with up to 1,000 users. Tax added at checkout where it applies.

No live sync (other devices get the latest copy when they load it), no queries or shared data (each document belongs to 1 person; load by name), no uptime SLA, no undo or old versions; anyone with the URL can read public bins, so no secrets or personal data.