Dueling Shows: With The Twilight Zone, though both were in production only during Twilight Zone's final season. In the end, Twilight Zone lasted for five years while The Outer Limits ended after two. On the other hand, the 1990s revival of The Outer Limits lasted nearly twice as long as both revivals of The Twilight Zone combined.
Franchise Killer: The original series was abruptly cancelled mid-way through the second season due to poor ratings, although it would gain another life in syndicated reruns, and get a long running revival series decades later.
Hey, It's That Guy!: Like most other genre anthologies, both series feature a host of recognizable actors, often before they became famous. There is at least one of these in EVERY episode, often two, sometimes three, and occasionally (like in the Showtime series finale) even more.
Vindicated by Cable: The first season was fairly popular in its day, but season 2's hit or miss quality (along with a fatal timeslot change) caused it to take a nosedive and be cancelled. Fortunately, the show managed to gain a decades-long life and recognition in syndicated reruns.
The 1998 version of The Outer Limits Companion includes an appendix which provides detailed plot synopses of TOS scripts and premises that were never filmed. It also has details on rewritten and Deleted Scenes from the finished episodes.
"The Forms Of Things Unknown" was written by Joseph Stefano with one eye on making it his directorial debut, but it ended up being helmed by Gerd Oswald (Stefano's only directorial effort came after he left the series, with the unsold pilot The Ghost Of Sierra De Cobre).