This calendar uses JSONBin (free, no credit card) so all family devices stay in sync. Setup takes ~2 minutes — only the first person needs to do this.
Step 1 — Get a free API key
Go to jsonbin.io/login, sign up (free, no credit card). Then open API Keys and copy your X-MASTER-KEY.
Step 2 — Create a public bin
Go to "Create New Bin", paste this exactly: {"visits":{},"messages":[],"helps":[],"swaps":[]}
Toggle the bin to Public, click Create. Copy the Bin ID from the URL.