Let's Encrypt vs Smallstep Certificate Manager

Let’s Encrypt is a global Certificate Authority that provides SSL/TLS certificates for HTTPS connections. The ACME protocol verifies control of a domain, and compatible clients can automate issuance, management, and renewal. Its client directory includes Apache HTTP Server, Caddy, nginx, Kubernetes, Docker, and Windows/IIS environments. Certificates are Domain Validation only; Let’s Encrypt says it does not plan to issue Organization Validation or Extended Validation certificates. Wildcard certificates are available through the DNS-01 challenge. Standard certificates last 90 days, with an optional six-day lifetime; these periods cannot be adjusted. Subscribers generate and manage private keys on their own servers. Issued and revoked certificates are publicly recorded, and the service says its certificates are trusted by most browsers and operating systems. Certificates cost nothing. A registered domain can receive up to 50 certificates every seven days under published rate limits. Direct subscriber support is not offered.

Smallstep Certificate Manager has no write-up on Specifiction yet; its figures are above.