The Wikimedia Foundation, which runs Wikipedia and its sister sites, has kicked off its annual fundraising drive with a US$500,000 donation from Google co-founder Sergey Brin and his wife, 23andMe co-founder Anne Wojcicki.

The foundation's total planned spending for the year ahead is US$28.3 million, most of which it will generate from user contributions.

Sue Gardner, executive director of the Wikimedia Foundation, says she hopes the donation will send a signal to other users.

"This is how Wikipedia works,” Gardner says.

"People use it, they like it, and so they help pay for it, to keep it freely available for themselves and for everyone around the world.

Wikipedia is the fifth most popular website in the world, attracting 477 million unique visitors around the world each month.

Other sites run by the Wikimedia Foundation include Wiktionary, Wikiquote, Wikibooks and Wikinews.

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