Slayer Planner

Open the Achievements window in game, press Output To File (or type /outputfile achievements in chat), and choose the file it writes (<character>_<server>-Achievements.txt in the game folder). This page reads it in your browser, nothing is uploaded, and lists your open slayer achievements by how many kills they have left, with the zones where the most of those mobs have been seen.

Achievements file

Zone figures count the spawn records seen there, so a zone no one has played in with the program shows nothing; a race the achievement names in a form the game's spawn records do not use is listed without zones.