Im happy to announce that I have started working on my new project called GTA Garage IV. It is going to be .net application that will allow you to quickly mod ingame vehicles as well as manage them later.
This is what I have done yet:
Everything seen on the screenshots is done and 100% working (except handling)
I want this tool to install vehicles in 1-2 clicks, make everything as easy and simple and it gets (many vehicles installing/removing at a time, drag&drop, easy handling editing, etc.) and create packages containing models, textures, handling, carcols, etc. that can be shared with other people using GTA Garage IV so you won't have to upload a whole vehicles.img.
Please feel free to share your thoughts about this project. Tell me what would you like to see in this app.
Also, if you want to contribute to this project even more you can become a beta tester or you can create icons (I'm bad designer).