One of the downsides of having data not stored on the platform is that the end users have to move between applications and logins to view data; this causes an overhead, as the process and data are not connected.

Salesforce Connect (previously known as Lightning Connect) is a chargeable add-on feature of the platform. It has the ability to surface external data within the Salesforce user interface via the so-called External Objects and External Data Sources configurations under Setup. They offer similar functionality to Custom Objects, such as List View, Layouts, Custom Buttons, and also Reports. 

External Data Sources can be connected to existing OData-based endpoints and secured through OAuth or Basic Authentication. Alternatively, Apex provides a Connector API, whereby developers can implement adapters to connect to other HTTP-based APIs. Depending on the capabilities of the associated External Data Source users accessing External Objects, using the data source can read and even update records through the standard Salesforce UIs, such as Salesforce Mobile and desktop interfaces.