KDE already have a many apps and some have the same features, for beginners it’s hard to choose the best app or app that frequently updated, because some apps already is not supported.
- Dragon Player?
- Plasma Camera
- Muon Package Manager
- KEuroCalc - Krunner is have the currency converter feature.
- Kontact - It's app with features from some other apps like KMail, KAddressBook, KOrganizer, etc.
I think it's not all, it's only that i found.