This thing is fucking magic.
It's ML autocomplete, with help from 'traditional' autocomplete methods that use static analysis. Instead of just completing one token at a time like traditional completers, it can do entire sentences or multiple lines of code in one go, and is freakishly accurate. And since it parses language it helps you write comments, and can understand relations between code. E.g. if you are writing 2d movement code and you do x += dx it'll automatically suggest y += dy for the next line based off of previous similarities; of course if you have x += [complex math formula] it'll fix it up for y and convert cos to sin, etc.
Support for many editors, and easy to install in vim. Free for personal use. Works for all languages, including plain English (and maybe other non-code languages?).