Tumblr founder and CEO David Karp keeps a sparce apartment in Brooklyn.

Net worth: at least $200 million

Karp founded the $1.1 billion blogging platform Tumblr as a teen, but these days, he leads a relatively simple lifestyle. His one big splurge: A 1,700-square-foot loft in Williamsburg, Brooklyn. He reportedly paid $1.6 million for the space, but half of that space is reportedly being unused.

"I don’t have any books. I don’t have many clothes," Karp told Forbes. "I’m always so surprised when people fill their homes up with stuff." He also loves to drive a Vespa.