Channel 4
(launched in 1982)
IMDb; official website; TV Tropes; Wikipedia

This is a British network that I've never seen directly, but I've seen some of its shows elsewhere.

stuff I've seen
Whose Line Is It Anyway? (9/23/1988 - 2/4/1999; aired on Comedy Central in the US; I've seen very little of this)
Ultraviolet (9/15/1998 - 10/20/1998; aired on Sci-Fi Channel in the US)
Alice Through the Looking Glass (12/26/1998; TV movie; I saw it on DVD)
The 1900 House (12/28/1999 - 7/3/2000; aired on PBS in the US)
Black Books (9/29/2000 - 4/15/2004)
Garth Marenghi's Darkplace (1/29/2004 - 3/4/2004; aired in the US on Sci Fi in 2006 and Adult Swim in 2007)
Electric Dreams (9/17/2017 - 3/19/2018; released on Amazon in the US)

stuff I want to see
Black Mirror (s1-2 + special; s3-5 released on Netflix)
The Camomile Lawn (miniseries; I saw at least some of this once, but I don't remember it well)
Elizabeth I (miniseries)
Humans
Lipstick on Your Collar (miniseries; I saw at least some of this once, but I don't remember it well)
Tales of the City (miniseries)