https://www.curseforge.com/wow/addons/instance-achievement-tracker
http://www.wowinterface.com/downloads/info24756-InstanceAchievementTracker.html
Join the discord to get updates about the addon. You can also report bugs there too or suggest new features.
WARNING: This addon is still a work in progress. I've added tracking for over 300 achievements, so there are bound to be some errors. If you come across any issues, It would great if you could report the issue in the comments below or on the discord server.
Instance Achievement Tracker helps track whether the criteria of achievements in raid or dungeons has been met or failed. All information is announced in the appropriate chat channel (raid, party, say) depending on the type of group you are in. Instance Achievement Tracker will also keep track of how many mobs are currently alive for achievements which require you to kill a certain amount of mobs in a time period. You can also easily see which players in the group are missing which achievements and announce tactics directly to the group chat.
/iat - Open and closes the GUI
https://discord.gg/achievements Tactics kindly contributed by the Achievements Discord Server, the community where members can meet like-minded completionists and form groups for a variety of achievements.