I recently started using the Solargraph LSP with neovim and it's pretty nice. Doesn't quite get you to the level of RubyMine in terms of smart-ness, but I find

I recently started using the Solargraph LSP with neovim and it's pretty nice. Doesn't quite get you to the level of RubyMine in terms of smart-ness, but I find it's close-enough in practice. And I also highly recommend using TreeSitter for syntax highlighting if you're gonna go the Neovim route -- for whatever reason, I've found regex-based highlighters to be unbearably slow on even medium-sized ruby files. I also work on a project that uses Rubocop for linting which is nice since it gives you some Prettier-like auto-formatting. There may be some more goodies to be had (e.g. debugging via nvim-dap), but I haven't dug into that yet. As it stands, I'm pretty pleased with my current setup.