Cliff's Notes versions
• RampantArcana has started a GitHub repository to codify the time-loop rules and the early-story timeline.
• Hawthornbunny has posted a chapter-by-chapter breakdown of all the loops, including the ones we don't see, with a lot of critical analysis.
If you're confused, either one of those fan projects is a great starting point, and story comments have a lot of insightful discussion as well.
Fan works
• "Do You Want To Kill Some Changelings?" [Lyrics] — RampantArcana wrote a song about the evolving relationship between Twilight and Celestia, to the tune of "Do You Want To Build A Snowman?" from Frozen.
• "Erred Earth's Re-had Easter" [Fanfic] — Prawo Jazdy's delightful HR2 homage explores what might have been, if the "easter egg" that I included in Chapter 11 had actually been a cryptic hint that Twilight Sparkle was going to start having some racial issues. NOTE: Currently this is included here (just click on the "previous chapter" link), but should be moving out to its own story soon.
• HR2 Movie Poster [Art] — I commissioned Alexstrasza for cover art, and Alex created this amazing homage to Die Hard 2: Die Harder. Looks even more awesome (and contains some easter eggs) at full resolution.