This is a complex extension. I've tested it with multiple groups for several weeks, but it's likely there are still bugs (please report them). Using the option to disable the extension should avoid most, but worst case you can restart your server after unselecting it.

Comments, bug reports, and suggestions are appreciated!

• It's event-driven, so most achievements are awarded as they are "earned". 
• The extension doesn't try to retroactively determine which achievements a character has.
• The DM can use the option's "Scan" button (or the "/ach scan" command in the chat window) to perform a in-depth check for some static achievements, such as playing on certain dates, or matching certain fantasy/historical characters.
• A few achievements (like killing a dragon) are earned by everyone in the party when they happen.

Some notes on scope:

• Some achievements are "within a session", which means that the triggers will be tracked during the session, but flushed when the host exits.
• Some achievements are "within an encounter". An encounter starts when a PC rolls init (unless it already started within the last 10 minutes). The encounter ends when the last foe is killed, or the party rests. It does not end when the session ends (since an encounter can span multiple sessions).

The extension works best if you set a DC for skill checks. You can do this on the Party Sheet, but a better way (if you want the players to roll, and to select specific players), is to use the wonderful Requested Rolls extension.

In general, using FG's features helps trigger achievements.  For example:

• actually using powers/feats/etc instead of just telling the DM
• distributing loot via the Party Sheet
• using Shift for Opportunity attacks

The Achievement Tracker doesn't depend on any other extensions, but some may help it check for certain triggers, such as:

• Pets
• Requested Rolls
• Undead Fortitude
• Aura Effect