Unofficial (almost unwritten) CPAN convention explains them as: 
    ::Simple    Simple/basic interfaces to more complex modules
    ::Lite      Lightweight implementations of protocols etc

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There's some overlap here. (Some people think SOAP::Lite should rather be SOAP::Simple.)

In reply to Re: *.pm vs. *::Simple by chromatic
in thread *.pm vs. *::Simple by Zecho

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