The Pittsburgh Pirates signed infield Pat Dorrian as a non-drafted free agent two weeks after the amateur draft ended. He's not your typical NDFA signing though.
Dorrian wasn't eligible for the draft because he signed with the Atlanta Braves as a 12th round pick in 2014 out of high school, before deciding shortly afterwards that he wasn't ready for pro ball. He left the Braves and went to college, though he was then ineligible for Division I ball since he already signed a pro contract. He attended Herkimer Community College for two years, then went on to Lynn University for the last two seasons.