Twine is an open source tool for buildig interactive narratives, choose-your-own-adventure stories, and point-and-click games. It has its own markup language, but users don’t need any previous coding knowledge, and the barrier to entry is very low.
Resources for Twine:
A trove of resources including tutorials, documentation, tools, etc.
How to Make Games with Twine by Auntie Pixelante
A step-by-step guide on getting started with Twine.
Guide to Twine markup.
Free Twine hosting for the web, so others can play your game!
Sample Module
Sample Games/Stories
“Ghost Burgers” by Anna Anthropy
“A Very Very VERY Scary House” also by Anna Anthropy