The Nicktoons channel back in 2004. It was awesome because it didn't show commercials, just classic Nick shorts and cool bumpers during breaks : r/nostalgia
Nickelodeon Shorts Available to Watch on Nicktoons site and app - Skwigly Animation Magazine
Nicktoons Film Festival - Wikipedia
NickALive!: Nickelodeon UK Launches "Short Toons" Animation Showcase On Official Nicktoons Website And Nick App