Kile is included in the Linux distribution at UiO. You can download it here: http://kile.sourceforge.net/
The LaTeX editor TexShop for Mac is included in TexLive. You can download it here: http://pages.uoregon.edu/koch/texshop/.
TeXworks (MikTeX) is included in the Windows distribution at UiO. You can download it here: http://www.miktex.org/