* is there an easy way to see what toolkit an application is using,
to be sure we aren't looking at applications that are using older
versions of QT or some other toolkit?
"About" -> "Qt" menu should work for most applications, I think.
Here, QJackCtl, for example, says: "This program uses Qt version
4.8.6". And if I remember correctly, a bunch of others Qt applications
have the same menu.