Before there was Google Photos, there was Picasa. Originally developed as a desktop app by Lifescape, Google acquired Picasa in 2004 and eventually added a photo sharing component called Picasa Web Albums.
But now Google is pulling the plug on Picasa.

The company says it will be retiring Picasa “over the coming months” to focus “one one service that provides more functionality and works across mobile and desktop, rather than divide our efforts across two different products.”
What does this mean for Picasa Web Album users? Not too much… all photos and videos uploaded to the service are now available for online viewing through Google Photos. Google will also provide tools for users to download their data, including tags, captions, and comments which may no longer be available).
What does it mean for users of the Picasa desktop app? You can keep using the software… but Google will stop supporting the application on March 15th, 2016. So don’t expect any new updates with bug fixes or additional features.