mosparo

mosparo is an open source spam protection system for forms. It catches spam submissions before they reach your inbox and is designed to be usable by everyone except robots: it works with screen readers and with mouse, keyboard or touch input, so nobody is locked out by an unreadable puzzle. The project comes from Switzerland and is released under the permissive MIT licence.

mosparo is self-hosted, so it is not necessarily European: you can host it anywhere, including on a server in the EU, where it becomes a free European alternative to the American captcha services. It suits site owners who care about accessibility as much as about spam.