Admin approval with some text that needs a little bit of thought to fill out is surprisingly effective and definitely slows down spammers a lot.

I had to do that on dbzer0 and I think beehaw, they were both a fun exercise and took no time at all. Hell, I ended up submitting a wall of text about Sacco and Vanzetti on dbzer0 if I remember correctly, lol. But if nothing else they knew that it was 1) a human, and 2) I really believe what I was saying.

If the point is to get regular users who are thoughtful participants in online communities, requiring an email address and the typing of a few coherent words on their own behalf is NOT a barrier to entry, or even a much of a bar. After all, these people are applying to join a forum in which they are presumably going to spend unlimited time typing statements of their own creation in the future. Instance owners are just requiring a bit of that up front, and it’s not a huge ask.

It is, however, a very frustrating requirement for people who want to open multiple accounts for spamming and trolling purposes, and for that reason alone is a great filter for applicants.