Although players may not be a free agent this offseason, about 200 players are eligible for arbitration. This means that the player and it's agent have the ability to negotiate the player's future earnings for the next year of the player's contract, based on how well the player has played in the past. This ultimately means that the player is getting a raise (in some instances the player may actually lose money). If a player has played well in the past but not in their arbitration year, they will likely receive less in arbitration. For low-buget teams, this can be gold becuase they are saving money on players who have had a good track record. In that event, the team will likely tender that player, and negotiate that player's raise. If a team decides that a player had a good season, and will likely receive a larger raise, they may decide to non-tender that player. Although the player's contract is not up, they still will become a free agent. The player who was non-tendered can sign with anyone, even his former team.
For example, John Axford is due for arbitration this winter under his current contract. Axford, who went 7-7 with a 4.02 ERA in 2013 could be a tough decision on whether the Cardinals want to tender him. If the Cardinals believe Axford is worth too much based on his performance, they could decide to let him test free agency. Axford could still sign with the Cardinals, but it come come at a reduced rate. If the Cardinals believe Axford is worth what his contract says, they could tender him, and give him a raise for the next year of his contract.
Sometimes it isn't about the money. Teams often non-tender players plainly because they just do not have enough 40-man roster spots in the upcoming season, and won't be able to hold on to their player.
Tomorrow, we will see some new free agents, and teams who decide to keep their players through the remainder of their contracts. Keep your eyes and ears open, because you never know who could be hitting the market.