Steam will allow you to curate certain portions of your library into the ether, either at time of purchase or later. It's also incredibly easy to do: you just right click on a game in your library, choose the Manage item from the dropdown, and choose Mark As Private. You can even do it with a shift-click group select, and do many, many games at once - a fact I mention just off-hand, for absolutely no reason, and not because it has any particular salience to my own intensely pure situation.
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