Toolkits
Highscores
Wurm Online Skillcompare (WOS)
Wurm Stats (WStats) - Discussion thread can be found here
Planning Tools
Mapper (By Discon)
Prospector (Used for finding the location of ores)
Housecalc (Used to calculate the required carpentry skill for wall plans and resources for houses)
Google Sketchup (Very popular and useful planner, and easy to learn. Helps aid builders visually with it's 3D detail. You can download tiles and house models Here, which all credit is due to Tich.)