Bill Leisner writes. Sometimes people enjoy reading what he writes. Sometimes (though not terribly often) people pay him for writing it.
Stuff he's been paid for writing includes the Star Trek: The Next Generation novel, Losing the Peace; A Less Perfect Union, a short novel in the collection Star Trek: Myriad Universes: Infinity's Prism; and the short story "The Year Without a Santa Claus" in the shared-world anthology ReDeus: Divine Tales.
Stuff he doesn't get paid to write? You're looking at it.