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The .sit is simply a compression method. You need Stuffit Expander (the expander is free) to uncompress it.

That said, I highly doubt that you can play them as almost all of the abandonware games need Classic to run and Intel Macs do not support classic.
 
You need stuffit program to unzip the files.

The basic stuffit is free.

*Edit*
*Beaten to it*

*Second Edit*
These games can't be played in intel Macs.
 
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