Aura framework
Aura is a framework for developing apps for mobile and desktop devices. In existence since 2013, Aura enables developers to build apps that are independent of data that resides in Salesforce, so development can be less disruptive to day-to-day users. Aura also enables efficient development because applications don't need to be optimized per device.
While the open source Aura framework underlies the Salesforce Lightning Component Framework, it also includes components that are not available in Lightning.