The secret to simplify what was usually very complex is that no code is needed to create applications: they can be created visually just by drag-n-drop. This makes it not only faster to create new applications, but also a lot easier to understand and modify existing ones. Other advantages are that all applications are deployed as open source .Net or Java code, they are managed centrally and can be published and rolled back with a single click with no data loss.
Check out this demo on how to create a web application in 4 minutes:
Recently OutSystems has also released a free version, the Agile Platform Community Edition, that lets anyone with a good idea to get down to business and implement it.