Rewind is a time machine for channels — choose a platform, type an account, pick a date, and get everything they published that day.
One day by default — fill the second date for a range.
Without a key, Rewind reads the channel's public RSS feed, which only exposes the 15 most recent uploads. A free key from Google Cloud Console (YouTube Data API v3) lets you search any date in the channel's history. The key lives only on this page while it's open — never stored, never sent anywhere but Google.