The biggest MLB free agents are still weighing their options, but teams have begun acquiring other players through trades. The Boston Red Sox and Atlanta Braves have made significant moves, and they are likely to make more in the near future.

Boston fell shy of expectations in 2015 and finished the year in last place, but they still hope to be contenders next year and are revamping their roster. Atlanta might not be good for a few years, and other teams will be the beneficiaries this offseason. Teams that had successful 2015 campaigns will be active, as well, as they look to stay near the top of the standings.

Below is a look at three teams to keep an eye on this winter.

Boston Red Sox

New Red Sox President of Baseball Operations Dave Dombrowski has wasted no time in looking to improve the team. He traded four prospects for San Diego Padres closer Craig Kimbrel, and Boston could be very active in free agency.

Boston signed two of the biggest offensive free agents last offseason, and the team will focus on the pitching staff in the coming months. With starting pitchers like David Price, Zack Greinke, Johnny Cueto and Jordan Zimmerman available, the Red Sox are considered possibilities for the best starters looking for contracts. Only the Detroit Tigers had a worse ERA than Boston in the AL, and Red Sox starters had a 4.39 ERA.

There have been rumors that Boston could look to trade one of their young players. But the likes of Jackie Bradley Jr. and Mookie Betts might not be going anywhere if the team can make impactful additions in free agency.

Atlanta Braves

The Braves don’t appear close to competing for a championship anytime soon, having won 67 games last season. As a result, the team has already started trading some of their best players, and there could be more moves to come.

Atlanta began unloading salary by trading Andrelton Simmons to the Los Angeles Angels, receiving Erick Aybar and two minor leaguers in exchange for the shortstop. Simmons was under contract through 2020, and the Braves are looking at trading “everyone owed money,” according to FOX Sports' Ken Rosenthal. That means Julio Teheran, right fielder Nick Markakis and center fielder Cameron Maybin all have the potential to be dealt.

Atlanta has reportedly shopped Freddie Freeman, who was easily the team’s best offensive player last season with a .841 OPS in 118 games. Freeman has hit at least 18 home runs in each of his five full seasons with the Braves. Right before the 2015 season began, the Braves dumped salary by dealing Kimbrel and Melvin Upton Jr. to the Padres.

New York Mets

After making their first World Series appearance in 15 years, the Mets are one of the favorites to win next year’s championship because of their star-studded pitching staff. But New York’s lineup will look a little different in 2016, and they are not expected to re-sign two of the most important hitters in their run to the Fall Classic.

Since trading for Yoenis Cespedes in July, the Mets showed little interest in holding onto the star slugger. With Cespedes potentially getting a $150 million contract this winter, that has not changed, and the team could lose their starting second baseman, as well. A team source tells the New York Daily News that it’s highly unlikely the Mets will keep Daniel Murphy, who turned down a $15.8 million qualifying offer for next season. Murphy could earn more than $60 million this offseason after an historic postseason run that saw him hit seven home runs with a 1.115 OPS.

Mets general manager Sandy Alderson has said the team's payroll should be slighlty higher than what it was last season, limiting opportunity to bid on a top free agent. New York could take a look at Ben Zobrist, who they might be more apt to sign than Murphy. Zobrist hit .261 against the Mets in the World Series, posting a .809 OPS in 126 regular-season games.