Game development: If you're already into browser game development, you are probably set to go; otherwise, you should know that there are plenty of JavaScript frameworks that can simplify the task. The first one that I can think of is Phaser, an open source desktop and mobile HTML5 game framework. With support for WebGL, canvas, physics, and tilemaps, it will make game development a breeze (http://phaser.io/).

System tool development: If you are planning to release a system tool, having a pretty good knowledge of Node.js/io.js is mandatory. That's something you can learn from books, online courses, and a lot of experience in the field, so there's not much I can tell you about it. However, once you've acquired the needed skills, you'll have to think about the look and feel of the application, so I'd love to introduce you to...