I'm going to develop an online website builder, aimed at general public (just like wix.com etc). Where people will Log in and create their website without having to do any coding stuff. They will create web pages and content by using drag & drop widgets and components. Once they complete their website, they will have option to publish it online on our servers or they can download the HTML files and host them on their own server.
I need to know if there is an existing open source solution? Preferably written in PHP, but I'm open to other suggestions as well.
I searched but found results like WordPress, Drupal etc., which is of course not what I'm looking for.