Early example of a successful virtual world that wasn't really a "game". More a space for people to explore / build / "live" in.
Transcluded from SecondLifeLandValueTax
Scott Santens notes that SecondLife is essentially funded by LandValueTax
"After a year, the company switched to a real-estate model. Anyone could visit for free, but those who wanted to own and shape pieces of the world had to pay. Land renters could do anything they wanted with their patch: erect a billboard, build a skyscraper, dig a mine, even run a company. 'That turned out to be a great business model,' @philiprosedale says. 'The people buying land were happy to pay for it because they were hosting other things on it, often to make money.'"
Second Life essentially runs on land value taxes, and not only that, but monthly subscribers receive a weekly stipend of Linden dollars. The world also applies a small fee to Linden dollar transactions.
So why has Second Life managed to stick around for so long? Perhaps at least part of the answer is that its economic rules are intelligently built.
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