I was looking for a joomla component that was not only a forms builder, but that permits to exploit databases. I found in LQM what I was looking for, because I knew already the sql language, that is the only necessity.
The way that this sofware is conceived offers (with a minimum of work) the possibility to built complete applications, passing from query results to other query by links, or menu options.
PHP code permits to go farther in possibilities (in header file ie). I didn't know this language but some samples can be customised to obtain desired result. The support on the web site is good and fast and the development of new features is continuous.