As many are aware, there is an online museum of programming languages called HOPL, which (sadly) is currently down while we change servers and seek funding. The Wayback Machine has some scrapes of the site for those interested. Wikipedia has many links back to HOPL. Unfortunately, these are all going to 404 until we can get things going again.
(The Wayback Machine has all kinds of cools stuff in its archive. Have you ever been trying to find a magazine article that used to be somewhere but isn't anymore? Wayback Machine!)
We have a shop window of sorts over on Facebook at HistoryOfProgrammingLanguages where we've been posting information, albeit sporadically, about languages, especially ones that currently are not in the main database. According to the main site, I'm the librarian in charge of 1990 to present. I'm am so far behind, it's not funny.
A couple of years ago, in a burst of energy, I posted Notes about some of the backlog. I hope very soon to have another burst of energy, but there have been so-o-o-o-o-o-o-o many languages developed since 1990. When I get back to it again, I'll also post here. Watch for "[HOPL]" in the subject line.