Take, for example, Jolt Online Gaming, which today launched its free-to-play casual web-based RPG Legends of Zork.
Inspired by the classic adventure series, Legends of Zork puts players in the role of an unemployed salesperson as they explore and fight their way through the fallen Great Underground Empire. It's a lot like Kingdom of Loathing, if you've ever played that.
Of course, there's a bit of a catch, albeit an optional one. By spending actual money or participating in a variety of marketing trials and surveys for other sites, players can earn coconuts, which will allow them to acquire more Action Points and other special perks. Those that don't pony up have to make due with their daily allotment of 30 Action Points.