Most of my layout is Kato Unitrack, but through the purchase of various starter sets or unique track capabilities, I've got a little bit of track from Tomix (primarily for their tight radius Tram system), Fleischmann Profitrack (that came with a starter set, but also for some excellent flex track), Minitrix and Atlas.
I thought it might be interesting to provide a few photo comparisons of two of those track systems that have roadbed that are not real well known in the US; Tomix Finetrack and Fleischmann's Profitrack. For reference, I'll also add in a piece of Unitrack (There are two other track systems in N Scale that I am aware of...the new Atlas track system [forgot the name] and the Bachmann EZ Track system)!
The photo at top shows, from left to right, the Fleischmann Profitrack, the Tomix Fine Track, and the Unitrack. Below is a close up of the Fleischmann and Tomix tracks:
As you can see, the Fleischmann is the narrowest, at just about 16mm, Tomix is a bit wider at 18mm, while the Kato Unitrack appears to be a hefty 25mm in comparison!
While they are all Code 80 - and thank goodness for that! - its fairly obvious that they will need a little effort to get to work together. Tomix, interestingly enough, seems to put its rail joiners on the opposite side of other manufacturers, and with that 'cast in' connector on the Tomix roadbed, some sort of modification (or a Kato Unitrack joiner for this purpose) is necessary.
A final shot below shows a side view....nothing spectacular here, except they all obviously work off different geometries (so you'll have to do some tricks to get them to work together somehow). While I have definite plans to use Finetrack for a tram system in my downtown remodel (103mm radius curves and accessories to make it look like rails in the street...although Kato appears to be right behind them!), Tomix is also coming out with a single track super-elevated curve! That will be cool and will require some big changes to my layout - but super-elevated curves are worth it!
I also have additional plans for the Fleischmann track...given its relative elevation to Unitrack, this would be great track for yards...although the cost of switches with motors in their system is crazy (E.g.: when it makes the Kato #4 switch look like a real value...its too much!).
UPDATE 5 December 2009:
Mel in the comments section is building a layout for his Grandson, and had a question about whether or not an adapter is needed for the Fleischmann track with either Atlas (code 80) or Minitrix track. Its a good question, and I expect other people will wonder as well!
Here's a couple of photo's of the three types: The first is the Minitrix track connected to the Fleischmann profitrack with just the standard rail joiners from each company:
While its not perfect, I don't know if any sort of adapter would help. Below is the Atlas code 80 track and Fleischmann:
The Atlas track as well works nicely with the Fleischmann track. The Fleischmann track is hair taller, but this can easily be addressed by a very thin shim. If it were me, I would not worry about an adapter. I recall reading somewhere that Trix does make an adapter, but I think this was for another track system (Rapido?) that I don't use.
Good luck on your layout project!