Hypos Tracks

Krom's MOX-Updater
This tool allows you to modify the mesh of a existing car and thus replacing the existing one. I'm sure that you can also include a brandnew mesh as long as you give it the same name. (Just open an existing mesh - replace it with yours and update. I haven't tested this though.

Unofficial Multiplayer by Racer_S 1.4b
This program allows you to play World Racing over TCP/IP with your friends! Includes a Client- and Serverprogram.

Krom's Mesh Toolkit v1.2
With this program you can import your own 3D Meshes into World Racing. So you can make now new cars or even replace the objects if you want.

Krom's Caredit Tool 0.7b
With this program you can edit the performancedata of the cars (and other things like tire-distance etc.).