Psychtoolbox is a popular open source tool for creating vision and neuroscience experiments. As typical of open source projects, the project mostly runs by a single, underpaid developer's time (Mario Kleiner). They tried to be funded through "support membership" donations, it did not work, and now they announce that a paid license will be required for running their compiled binaries "on some operations systems".
The relevant part where they describe the funding situation of the project starts around 6:00 as in https://youtu.be/05gpkP_EMoc?t=363 (sorry for messing up the link in the post)