Corel Linux from 1999. It was a Canadian Linux distro by Corel Corp (now Alludo/Cascade Parent Limited). It was clean and easy to use distro based upon Debian and KDE. More about this distro @ https://en.wikipedia.org/wiki/Corel_Linux
@nixCraft I think this was the first distro to add support for putting the taskbar in the main panel like KDE 2 and later. KDE 1 did not have that by default afaik.