Not similar to HN, if you mean a replica like Lobste.rs. Then again, the following communities have reached some critical user count: - https://mathoverflow.n

Not similar to HN, if you mean a replica like Lobste.rs. Then again, the following communities have reached some critical user count: - https://mathoverflow.net/ https://mathoverflow.net/ - https://biology.stackexchange.com/ https://biology.stackexchange.com/ - https://physics.stackexchange.com/ https://physics.stackexchange.com/ - https://chemistry.stackexchange.com/ https://chemistry.stackexchange.com/ There are lots of scientists on HN, though.