Authoring

CardStock

Callooh! Callay! A HyperCard clone that doesn't suck AND has programming in Python (rather than HyperTalk). Brilliant!

Twine

Write interactive narrative fiction (the online version). Create your own adventure game!

Hatch

Authoring

Excellent little multimedia tool for creating interactive thingies. Has stickers, effects, gifs etc.

OctoStudio

Fabulous Scratch-based authoring system (on mobile) that has better connection to the devices gyroscope, camera, light etc.

Downpour

Fun mobile app (Android, iOS) with which you can make quirky games.

A Frame

A web framework for building virtual reality experiences

WickEditor

Fabulous web-based animation and game-making tool

Aframep5

A brilliant Javascript p5js library that is integrated with A-Frame so that you can generate A-Frame objects but using the more familiar format of p5js.

Alice 3

Amazing 3D tool. You can create scenes and interactions using Scratch-like coding.

Based on Hypercard, this web-based authoring tool looks great. Except the Lil language is, er, not to my taste at all... And you can't (or I can't) just make a stack's size to be fullscreen... and why the hell does the UI fetishize Hypercard, rather than ape it brilliance. I could imagine making wonderful 1bit stuff with this, but it's LOCKED into recreating zombie Hypercard stacks rather than giving them new life. (imo)