Dating back as far as ancient Egypt, Tic Tac Toe (also known as Noughts and Crosses or X's and O's) is a classic. It's also quite simple to develop, requiring only a basic knowledge of conditionals, loops, and similar programming concepts.
Here, I've put together a version that can be played on any device with an Internet connection and a web browser. Just visit my Heroku deployment to play it yourself.
The game is developed using Node.js (express), socket.io, and HTML5 canvas. Clients connect to the server which hosts the current game state and submit inputs by clicking or tapping on a space on the board. The server processes that input and updates the board accordingly.
This was a simple project where I wanted to be able to make a cross-platform app. HTML5 powers the client-side, Node.js powers the server-side, and socket.io connects the two. These technologies make it easier than ever to put together a web app and deploy it. Thanks to Cloud 9 and Heroku, I don't even have to host a server.
Going forward, I'm hoping to use this foundation to start building similar web games that are cross-platform. You can see my progress on GitHub and also view my previous project Paint the Floor.
Thank you for your time.