Zooniverse

Real research that needs human eyes: classify galaxies, transcribe war diaries, count penguins. Contributors are credited in published papers.

Who can enter: Anyone worldwide. Free, no account needed to start classifying
What it costs: Free, and run by a university-led collaboration rather than a company. Nothing is sold at any stage.
When it closes: We could not confirm this year's date against the organiser's own page, so we are not showing a countdown for it. Last published: Open all year: pick a project and start, free.

Sending this to someone sends the four facts above, not just a name. They will see who can enter and what it costs before they decide.