Many people are concerned about standards in written English and have produced similar websites, and all credit to them. I think all though adopt what I think is a confusing multi-rule approach. I hope you can see that the consistent one rule approach adopted on this site fits all the examples given on other sites.
The Apostrophe Protection Society
The Apostrophe - Ottawa University
Punctuation Made Simple - still not simple enough though.
Sharon Colon's Apostrophe Page - some nice pictures of straying apostrophes
Problems with apostrophes - Paul Doherty's take on this.
There are many more - just Google "Apostrophe". But they all insist on you learning at least two separate rules. But you know now there's really only one.
World Wide Words - a fascinating compendium of linguistic lore which one can browse for far too long!
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