What build tools are you using - npm, gulp, webpack, grunt?

I still find myself using various npm packages to build my code; check for syntax errors; linting; style guide adherence; bundle and minify css and js code. Task runners are a more improved way to automate these tasks. What tools are you using and how do they help with increasing your productivity?

I use one tool. CodeKit. It does everything you mentioned and some more.

https://codekitapp.com/

About a year I use webpack, before that gulp, before that grunt.

I notice that Webpack in now number 1 and with the recent release of 4.0, I suspect they may remain the front runner. When I get some time I want to move an old gulp script to Webpack I would be a great learning experience to compare and contrast their respective approaches.