PsychoPy is a free cross-platform package allowing you to run a wide range of experiments in the behavioral sciences (neuroscience, psychology, psychophysics, linguistics...)
This is a community project. Users have all the source code. Users are the developers. Users support each other
Alongside open-source, we're strong supporters of Open Science, and we'll try to encourage and facilitate that wherever we can!

Easy enough for teaching

Universities all over the world are using PsychoPy for teaching students about experiments

• Flexible and intuitive Builder interface to create huge range of studies
• Textbook(s) suitable for both undergraduate and professional audiences
• Many further resources for learning and teaching, including Youtube tutorials, online tutorials and workshops
• The Pavlovia repository of shared experiments accessible directly from the application (requires PsychoPy3) to search for and share your studies

Precise enough for psychophysics

Hardware accelerated graphics, best-in class timing, and calibration tools built in

• Fantastic timing precision (see the timing mega-study for comparisons)!
• Time and update your stimulus on every screen refresh!
• Tools to help monitor calibration and wide range of units
• Hardware-accelerated graphics for stimuli that can be updated on the fly
• Access to button boxes when you need the utmost precision
• Automated logging for you to what happened and when
• OpenGL (and shaders) ready for use when you low-level access to graphics

Flexible enough for everything else

PsychoPy is great for:

• Dynamic, interactive studies: Free yourself from simple static stimuli! You can update your stimulus interactively on every screen refresh!
• Neuroimaging: Send and receive triggers to your hardware at precise times
• Eye-tracking: Access to wide range of hardware (eye trackers, button boxes, trigger systems...)

Online

Want to run your study on the web, so users can access it anywhere?
PsychoPy3 added the facility to run studies online using a high-performance, hardware-accelerated, port of the PsychoPy Python library

• Export your experiment from Builder to a web page
• PsychoPy is the only package with reaction time precision under 4 ms online!
• Update your stimulus on every frame, just like in the desktop!
• Upload that to Pavlovia.org (with easy tools built into the PsychoPy app)
• Give participants your URL and run your study in the browser!
• You can recruit participants using Sona, Prolific, Mechanical Turk or similar systems