Expirity checks domain expiry (RDAP/WHOIS), full DNS record sets, nameservers, and SSL certificate status on a schedule (daily on the free tier, near-real-time on paid), and writes a change log every time something differs from the last check - registrar change, NS change, new/removed DNS record, cert reissue, etc. Alerts go out by email, Slack, Discord, or WhatsApp. There's a REST API and CSV/Namecheap/GoDaddy/Route 53 import if you're bringing in an existing portfolio.