These are one trick ponies. People will read about a language, search for an online interpreter, try something out then
leave. More people will want a web REPL for an esoteric language than a nostalgic one, I think, for two reasons:
Esoteric languages are usually simple. You can learn one from a wiki page and start writing toy programs right away. Nostalgic languages have higher barriers of entry.
They are also typically unusual, so people would often wonder how they can work at all. Nostalgic languages usually do not cause this reaction. When I read about Smalltalk on the wiki, I certainly don't think "oh, I wonder if I can try
it out online", unlike the case with Brainfuck.
So far we have 2/5 in this category, Brainfuck and LOLCODE. Both are fully featured.
Notable esoteric languages include:
Bloop/Floop. Although not very REPL-friendly (being procedural), it is somewhat reasonable and mentioned in a popular book ("Godel, Escher and Bach"), so there should be a decent number of people who will be interested in it.
Unlambda. Purely functional so very REPL-friendly; simple to implement.
These are one trick ponies. People will read about a language, search for an online interpreter, try something out then leave. More people will want a web REPL for an esoteric language than a nostalgic one, I think, for two reasons:
So far we have 2/5 in this category, Brainfuck and LOLCODE. Both are fully featured.
Notable esoteric languages include:
Less notable languages to consider:
On the whole, filling the quota here won't be a problem if we really want it.