k3b - died with the cd-rom

calligra office - creation of LibreOffice stole the thunder

konqueror - maintaining a secure browser that isn't a fork of chrome is a tall ask these days

amarok / kmail - rewrite lost features, introduced bugs, and many existing alternatives filled the gap

That said there are still a lot of good ones still there that continue to improve every day. Kate, dolphin, KDE connect, etc.