Zuckerberg's first endeavor was a music recommendation platform called Synapse.

Zuckerberg has been working on side projects since he was in middle school, when he developed a basic messaging system that allowed computers in his home to communicate with each other.

As a high schooler, Zuckerberg explored an even more ambitious side project, a music platform called Synapse.

"As students at Phillips Exeter Academy, Zuckerberg and friend Adam D'Angelo created an MP3 player that would keep track of every song the user played on a computer and, as it learned what the user liked, would begin to make playlists," the Harvard Crimson wrote in 2003.

According to the Crimson, Zuckerberg said he and D'Angelo were offered nearly $1 million for Synapse, but they turned it down.

"One of the companies offered us $950,000 but wanted us to go work for them for three years," Zuckerberg told the Crimson. "We wanted to go to college, so we said no."

The future CEO added that they wanted to keep the platform free for users.

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