The Ad-hoc Designer is a completely browser-based application (HTML and JavaScript) that allows you to design basic reports like simple tables or charts very quickly. It offers only the most important features of the full List & Label Designer, but does not require an installation on the client computer like the Web Designer does. Furthermore, it provides a simplified user interface that can be used on any modern device, operating system and browser.
The Ad-hoc Designer is not a replacement for the List & Label Designer or the Web Designer.