There's a bunch of plugins like that, here's a couple of the most popular ones:
- https://github.com/prabirshrestha/asyncomplete.vim
- https://github.com/lifepillar/vim-mucomplete
- https://github.com/prabirshrestha/asyncomplete.vim
- https://github.com/lifepillar/vim-mucomplete
Note that mucomplete isn't async, it's intended to be simple.