Acrozilla and AcroChallenge have much in common - and some significant differences, too.
This page highlights those differences.
Differences from Acrofever page.

How Acrozilla Differs from Acrochallenge

    New, improved features:

  1. Easier to find a mistake in your acro as the letters turn green when matched.
    Explict message in chat telling you why an an acro wasn't accepted.
  2. Notifications of votes or acros which are submitted after time runs out.
  3. Occasional wildcard 'letter' appears as asterisk, matches any word.
  4. Never more than 2 of any letter in the acro letters.
  5. If yours is the only acro in the round, you can win points even though it was impossible for you to vote.
  6. All games visible in the lobby, without any intermediate levels.
  7. Ability to stay in a room in non-playing mode to avoid holding up the game.
  8. Players automatically put into non-playing mode if two complete rounds missed.
  9. Games are paused if there are no active players (only watchers).
  10. Simpler private message syntax: @player rather than /pc player\ (because spaces not allowed in player names). The Acrochallenge syntax is accepted though.
  11. You can reply to a private message (or follow up one you sent) by clicking it.
  12. Clicking a players name in the score list sets up a private message.
  13. /games command or clicking an icon shows you all the active games in a popup graphic rather than chat lines (and you can join one of those games with a click).
  14. You can see your own acro during voting (but still cannot vote for it).
  15. For non-voters, the number of votes they received is displayed (along with 0 points).
  16. Support for Story Time games: Title round and default "Continue the story" topics automatically supplied, as are Story recaps.
  17. Support for Topics by Creator: can preload a whole set of topics after game is set up.
  18. "Word Acro" style games - where the letters spell a word which is also the topic.
  19. "Picture Acro" - where topics are pictures instead of phrases/questions
  20. Logging of scores and acros, for, say, a league table.
  21. Recognition of more high scoring acros ("Double Digit Club" vs player's single highest scoring acro shown in profile), without limit on a player's tenure.
  22. Different scoring: Bonus points are based on the number of votes received rather than the number of letters/words of the round.
  23. Simpler process for creating a game, with fewer options.
    All games are 10 rounds, and maximum players is 12.
    No faceoff option provided.
  24. A much broader range of over 1000 2000 3000 (and growing) server supplied topics, with date-based additions for holiday seasons.
  25. Simpler re-submit process for acros: Just edit and hit Enter.
    If you want to take back an earlier entry, there is a "Revoke" button.
  26. If you have no acro for a round, you can click "I got nothin" button to save some time.
  27. If you return to a game after a disconnection, you keep your points.
  28. Less likelihood of disconnection in the first place.
  29. Ability to have online moderators who can deal with troublemakers effectively.
  30. Room creator can /boot a troublemaker and keep him from returning.
  31. Sounds to indicate start of round, acro submitted, and 10 seconds of acro time left. Option to turn them all off (collectively).
  32. Diverse background images for holidays and throughout the year
  33. Available only during limited hours (vs 24/7, when it isn't down).

A few things AC has that AZ lacks (for now at least).