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Get Games has a couple of weekend sales up.
Borderlands Mac Weekend
Borderlands 2 $5 (Steam)
Borderlands 2 GOTY $10 (Steam)
Borderlands 2 Season Pass $7.49 (Steam)
Borderlands 2 DLC 75% off. (Steam)
Borderlands: The Pre-Sequel $24 (Steam)
Borderlands: The Pre-Sequel Season Pass $10.19 (Steam)
Borderlands: The Pre-Sequel DLC 50% off. (Steam)
All of the above titles are Steamplay so they will activate the Mac versions also.
F1 2015 Release Sale
F1 2010 $5 (Steam)
F1 2011 $7.49 (Steam)
F1 2012 $10 (Steam)
F1 2013 $13.49 (Steam)
F1 2013: Classic Edition $17 (Steam)
F1 2014 $17 (Steam)
F1 2015 $46.74 (Steam)
F1 Race Stars $5 (Steam)