General - https://www.katacoda.com/learn
SQL - mystery.knightlab.com
CSS - flexboxfroggy.com GIT - https://ohmygit.org VIM - https://vim-adventures.com/ Command Line - https://github.com/veltman/clmystery Concurrency - https://deadlockempire.github.io/
Python - http://www.pythonchallenge.com/