One popular tech site in Russian was invite-only for a very long time: https://habr.com https://habr.com I remember you could get in by someone inviting you or

One popular tech site in Russian was invite-only for a very long time: https://habr.com https://habr.com I remember you could get in by someone inviting you or if you wrote a good guest post (there was a separate area for this kind of guest posts and no one could see who the author is). I got impression that invite-only system worked quite well as the site was known for high-quality content and discussions.