With respect to the crashes on Macs that have been around since roughly September 3rd, try installing the latest Steam beta update, in accordance with the following steps, please:http://steamcommunity.com/sharedfiles/filedetails/?id=182912431
If the above doesn't help, send us a support ticket including the following:
A detailed description of the problem. If message pop-ups,
error codes or other notifications are displayed, copy their content or
attach a picture (screenshot), please.
A System Information report generated on your system.
Here are the steps for you to follow in order to generate the report:
- Open the "System Information" application
- Press the "System Report..." key
- Use "File -> Save..." or "⌘S"
- Save the generated report on your drive