KDE is the desktop and window manager based on QT, so having QT is very close to Maemo and Symbian based on QT. On top of KDE are applications like KOffice (KWord, ..) just ported to Maemo 5, and the internet browser Konqueror...
I found www.wikipedia.org very good in explaining KDE, XFCE and differences between distros. Maemo and Ubuntu are Debian-based.