I got an educational copy of Pro/ENGINEER from
JourneyEd. It really is pretty amazing...I was used to AutoCAD, and Pro/E blew me away. It's available for Windows, by the way; I have used it quite happily on Millenium and now XP. (The educational version, by the way, is fully functional; it just includes something that means files from the educational and standard versions are not interchangeable; it also adds a small 'For Educational Use Only' to drawing printouts).
The main feature of Pro/E is that it is fully parametric. Parts are created using 'features', each of which is dimensioned from datum planes and existing features. You can change any dimension of any feature, and all the features based on it will automatically change. One very nice feature, especially for FIRST, is the ability to quickly create 'part families' of similar parts such as a bunch of different sizes of gears, nuts, bearings etc; you create the basic part, specify which dimensions change among different versions of each part, and then just dump in a big table of values (often I can just copy and paste out of PDF catalogues).
Parts are then brought into assemblies. You put parts together according to how they should really fit together, not using dimensions; for instance, to start a gearbox, I place a motor, then bring in a gear and say it should be in a vertical plane through the motor, the front faces of the motor pinion and the gear should be aligned, and the surfaces should be tangent. Again, everything is parametric, so if that first gear is replaced by, say, another gear from the same part family, everything else moves so all the placement constraints (mate, align, insert, tangent etc.) are still satisfied. Part families are very nice in asemblies; once you've built up a library of the standard parts you use, assembling them together into gearboxes and other stuff becomes very, very quick.
There's just a massive amount of other features, too...built-in standard hole sizes for imperial and metric (including countersink and counterbore, if you want), a 3D model that's always fully rendered, the ability to simulate and test the mechanics of your models, sophisticated measurement tools (dimensions, inertia, mass...), an animation option (simple), a massive sub-program for creating engineering drawings with projections, details, cross-sections, bills of material....pretty much every time I've wondered 'Can Pro/E do this?', the answer has been 'Yes'.
Unfortunately, the massive power of the program (the commercial version is $34 000) comes at the expense of usability - Pro/E is quite hard to learn and can be quite finicky, especially with file management and especially in Windows, by the looks of it.
Has anybody used Pro/E alongside other programs like CATIA, SolidWorks, or Unigraphics? I have never used any of those programs, and I would be curious to see how they compare.