Out of the Park Baseball is a great baseball sim....not free
Become a GM of a francise and you can control everything from the major league roster all the way down to AAA, AA, A rookie ball and the draft.
Uses 20-80 scale scouting of players for a hugh variety of attributes from hit skill, power, fielding, speed etc.
Can also set the level of control to allow computer to run minors while you control major league club.
Plenty of downloadable content. Create custom leagues, use historic players like Ruth, gehrig, Williams etc.
Bottom line if you are into baseball it has it all. Can play game by game or sim seasons in minutes