Kate is a multi-document editor part of KDE since release 2.2. Being a KDE application, Kate ships with network transparency, as well as integration with the outstanding features of KDE. Choose it for viewing HTML sources from Konqueror, editing configuration files, writing new applications or any other text editing task. You still need just one running instance of Kate.
With a multi-view editor like Kate you get a lot of advantages. You can view several instances of the same document and all instances are synchronized. Or you can view more files at the same time for easy reference or simultaneous editing.
KWrite is a simple text editor application, allowing you to edit one file at the time per window. As Kate, KWrite uses the editor component KatePart. KWrite simply provides the selected editor component with a window frame, and lets you open and save documents. KWrite shares all features the KatePart provides, look here to get an overview.