Old Standard and Theano Didot are two of the most interesting free unicode fonts containing polytonic Greek.
Old Standard was intended as a multilingual font family suitable for biblical, classical and medieval studies as well as for general-purpose typesetting in languages which use Greek or Cyrillic script. It reproduces a specific type of Modern (classicist) style of serif typefaces, very commonly used in various editions of the late 19th and early 20th century, such as Teubner, but almost completely abandoned later.
Theano Didot contains polytonic Greek, and Latin. It is a well designed font you will find inspiring if you work with Greek texts. Theano Modern and Theano Old Style (variations included in the Theano download package along with Didot), can be useful in some occasions, but Theano Didot, along with the other font, Old Standard, are most probably the ones you will need regularly.
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