deoplete.nvim
Dark powered asynchronous completion framework for neovim/Vim8
...It was designed to provide extensible code-completion behavior while avoiding the blocking feel of older synchronous completion plugins. The framework can display completion candidates through Vim’s built-in completion interface and can be extended with dedicated completion sources. It supports a plugin ecosystem where different languages, tools, and contexts can provide their own candidate sources. deoplete.nvim is useful for users who want configurable, editor-native completion without adopting a full IDE. Although newer completion systems are now more common, it remains an important project in the evolution of asynchronous completion for Vim and Neovim.