Authy vs Duo: What are the differences?

Authy: The easiest way to add Two-Factor Authentication to any website or app. We make the best rated Two-Factor Authentication smartphone app for consumers, a Rest API for developers and a strong authentication platform for the enterprise; Duo: A next-generation package manager for the front end. Duo is a next-generation package manager that blends the best ideas from Component, Browserify and Go to make organizing and writing front-end code quick and painless.

Authy belongs to "Security" category of the tech stack, while Duo can be primarily classified under "Front End Package Manager".

Some of the features offered by Authy are:

• Very secure- We take security seriously. We use industry standard secure algorithms (HMAC RFC 4426) and 256 bits keys which are always encrypted at rest.
• Fully redundant- The Authy API is deployed accross different PCI level 1 data-centers and it's fully redundant. We also use a DNS provider with anycast support. We've had 100% availability since 2011.
• Great user experience- You connect to Authy using a transparent REST API which allows you to customize the experience you want for your users.

On the other hand, Duo provides the following key features:

• has first-class support for Javascript, HTML and CSS
• exposes a unix-y command line interface
• pulls source directly from GitHub with semantic versioning

Duo is an open source tool with 3.52K GitHub stars and 145 GitHub forks. Here's a link to Duo's open source repository on GitHub.