Star Trek "The Animated Series"

After the much lamented cancellation of the original Star Trek series in 1969, NBC reprised the show in a half-hour animated format with almost all of the cast of the original. The animated format allowed a much greater freedom in alien forms and "special effects" so to say.

Episode two, "Yesteryear" uses the same time travel gateway featured in the live action City on the Edge of Forever. In this story, Spock returns from a historical survey to find that the past has changed, and he had died at 7 years of age. Written by DC Fontana, this episode shows the promise of the format. Unfortunately the series was cancelled after only 22 episodes. Luckily they are available in DVD format, and you can watch all the episodes here at YouTube. A synopsis of all 22 episodes is available at Wikipedia.

Other notables are the Episode The Slaver Weapon, based on Larry Niven's "Known Universe" short story of the same name, and the use of the "holodeck" in episode 19, The Practical Joker.

Here is part I of Yesteryear at YouTube: