Despite its ease of use, Testable is comprehensive and versatile.
It can display images and words, play sounds and movies, and create surveys.
The response options include stimuli clicks, button clicks, key presses, free text input, pixel and quadrant coordinates for mouse clicks. Even voice responses!
All standard experimental parameters, such as presentation times, inter-trial intervals, inter-stimulus intervals, response windows and many more are customisable.
Testable allows for simple and advanced randomisation within and between blocks, and easy between-subjects experiments.
Some of the advanced features (many which you cannot find anywhere else) include our multiplayer environment, staircase procedure, and real-time data visualisation.

A little more info on Testable...