Duo Security vs OpenSSL: What are the differences?

Developers describe Duo Security as "Verifies the identity of your users with two-factor authentication". In order to trust that your users are who they say they are, we verify their identity with an easy-to-use two-factor authentication solution, while giving you the ability to enforce stronger user access policies. On the other hand, OpenSSL is detailed as "Full-featured toolkit for the Transport Layer Security and Secure Sockets Layer protocols". It is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. It is also a general-purpose cryptography library.

Duo Security and OpenSSL can be categorized as "Security" tools.