application (to take part in); registration
entry qualifications; joining qualifications
free-for-all; open-to-all; optional (to participate in); non-compulsory
entrance fee; participation cost
participation award; prize for participation
those interested in participating; persons wishing to participate
participatory; participating; hands-on
possibility of participation; participation possibility
you are cordially invited to participate; please come and join us
to call for somebody's participation
free-for-all; open-to-all; optional (to participate in); non-compulsory
participation in politics; political participation
capital participation; equity participation
attending a meeting; participating in a meeting
labor participation in management (labour)
audience participation program (programme)
auxiliary intervention (in a lawsuit)