Here's my set of concentric circles on Koine Greek and its close relatives with a bit of commentary and some resources for each in Greek (where readily available), moving out from the centre:
- LXX and NT : there's plenty already around on this, so suffice it here to note the (probably) lesser known volume (only one of a projected set) by Henry St. John Thackeray, [A Grammar of Old Testament Greek according to the Septuagint][hsjt] (Cambridge, 1909). (Due to be superseded by current projects on this front, but still useful.)
It is worth bearing in mind that there are gradations of language/register, even within this body of literature. Things like Greek Jeremiah, or the gospel of Mark, are less refined than Greek Isaiah or Proverbs and the gospel of Luke. Within the "Apocrypha", too, a continuum can be seen: Tobit and Judith are relatively simple; the additions to Esther more "literary", and 3 and 4 Maccabees are getting much closer to "Attic".
- Apostolic Fathers : as they're usually c