Classic examples include marketplaces that match buyers and sellers, payment networks that link cardholders and merchants, and app stores that connect developers and users. The platform succeeds when both sides show up in balance; too few of either weakens the offer for all.
Design centres on cross-side network effects and pricing. Operators often subsidise one side to attract the other, and invest heavily in matching, trust, and quality so interactions are worth repeating. Achieving critical mass on every side is the hard early problem.