File explorer is one of the most widely-used types of plugin for Vim/Nvim. Below are my curated list of file explorers for Nvim. Some of these plugins are specifically written for Nvim and will not work for Vim.

nerdtree
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vim or Neovim: both
platform: Windows, Linux, macOS
feature: rich feature with a lot of mappings
speed: slow for large directory

fern.vim
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vim or nvim: both
platform: Windows, Linux, macOS
feature: rich feature
speed: implemented in vim script, asynchronous operation so maybe fast

vim-dirvish
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vim or nvim: both
platform: Windows, Linux, macOS
feature: not very rich, concise without many decoration
speed:

nvim-tree.lua
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vim or nvim: nvim only
platform: macOS, Linux, Windows
feature: seems complete
speed: quite fast, but for large number of files, there will be some delays.

tree.nvim
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vim or nvim: nvim
platform: Linux, macOS (author claims to support Windows, but no install script available)
feature: medium feature
speed: haven’t tried, written in C++, maybe very fast

defx.nvim
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vim or nvim: both
platform: Linux, macOS and Windows
feature: very rich
speed: haven’t tried, but may be fast due to python implementation.

chadTree
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written in Python (requires at least Python 3.8.2)

vim or nvim: nvim only
platform: Linux, macOS and Windows
feature: very rich
speed: asynchronous and fast

lir.nvim
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vim or nvim: nvim only (written in lua)

telescope-file-browser.nvim
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vim or nvim: nvim only
platform: Linux, macOS and Windows
speed: asynchronous and fast (seems to be faster than nvim-tree.lua, I have tested both on a directory with 100000 files)
misc: It is an unconventional file explorer. It uses telescope floating window for file management.