Just to take one example, one might build a service where users invent board games. This could be done using human-based genetic algorithms: http://en.wikipedia.org/wiki/Human-based_genetic_algorithm. Users of the service would be able to modify rules to try to make a game more fun. A fitness function would take into account how popular various game variants are among players. Note that users of such a service need not be programmers: the domain is sufficiently restricted so as to make visual point-and-click rule creation/modification possible.