Well, actually there are quite a number of software for parametric modelling which you could consider, the list of which can be found below. The 3D authoring software field is still pretty diverse with different tools being great for different applications.
Here is list of free CAD software packages you can try
1. AutoCAD Student Version
AutoCAD, for free?
Yea, you read that right. AutoCAD, the heavy hitter of the CAD industry, offers a free, fully functional, version for download to students, and anyone who is unemployed that has previously worked in the AEC industry. The only limitation of the software is a watermark on any plots you generate designating that the file was created with a non-professional version.
Not only does Autodesk offer their base AutoCAD package free, they also offer free licenses for almost their entire suite of AEC vertical packages, such as Civil 3D, AutoCAD Architecture, and AutoCAD Electrical.
If you're looking to learn CAD or just do some personal design work, this is absolutely the way for you to go.
2. Rhino 4.0
Rhino 4.0 is a 3D modeling software that I find very easy to use. It's got basic solids and the ability to form unions and free sketch in polylines that can be easily converted to 3D objects. The only thing I don't like about Rhino is that it's a limited use download. You can only save 25 files before the save feature is disabled. Still, it's a great way to practice 3d modeling, just make sure you don't save unless you absolutely have to!
The free version of DraftIt is a very basic CAD system. I wouldn't recommend it for trying to do any serious design work but for anyone who's looking to learn CAD or just do some basic sketches for your new bathroom layout, it's a workable system. I do have to say, there's one command here that really impresses me: offset. It's a common CAD command but I love that you can hit a check box that lets your offset to both sides of an object at the same time with a simple drag of the mouse. Check it out, its very cool.
DraftSight is a truly free software package that is ideal for individual use. There are no fees or limitation on usage or plotting. The only requirement is that you need to activate the program with a valid e-mail address.
DraftSight is a basic 2D drafting package that looks and feels very much like AutoCAD. It has all the drafting tools you'll need for generating professional looking plans: lines and polylines, dimensions and text, and full layering capabilities. DraftSight even uses the .DWG format as its file type, the same as Autodesk products, so you'll have the ability to open and share files with other users.
5. Google (Trimble) SketchUp
SketchUp is one of the greatest free CAD packages ever put on the market. The free version has no limitations and it provides one of the simplest 3D design interfaces I've ever seen. Even if you've never done any CAD work or 3D modeling before, you can have some really nice presentations put together in minutes.