One free agent who is still out there: Johan Santana, winner of two Cy Young Awards during his brief but brilliant tenure with the Twins
Santana hasn't pitched in a competitive game on any level since 2012 other than two innings in a winter league game in 2015,, but he's always found somebody willing to take a flyer on him. His Mets contract expired after the 2013 season. He signed with the Orioles for 2014. He signed with the Blue Jays for 2015. His rehab programs never got to the point where he could take the hill for either organization,
When the Blue Jays released him last June after a foot infection halted his rehab, the word was that Santana intended to pitch winter ball. As far as I can tell, that didn't happen. He certainly hasn't found a team that thinks him worth the rehab investment this year. Considering the long layoff, considering that he turns 37 this month, that's hardly surprising.
So this may be it for Johan Santana. If so, he becomes just another player who baseball let go before he was ready to let go of baseball.