Wirsbo, now known as Uponor is the only one that used the PEX ring over the pipe.
Rehau was the only one that used the APR type system that USP45 is describing. They let the patent run out or whatever and Uponor jumped on the APR bandwagon too.
Rehau also has the copper crimp ring method. Then there is the stainless steel band method as well as Viega's stainless steel sleeve method.
Of course Kitec has their own propietary crimp ring method as well as their own compression method. And then a lot of different manufacterers had their own compression fittings too.
I think I am missing a system or two but I basically have them covered here.
Uponor's system that herk is describing is where you slip a ring made out of PEX over the end of the PEX, make it flush with the end of the pipe, expand it and slip it over a fitting. It's a good method and in my opinion the next to best method.
But the APR type fitting system which USP45 is describing is much better. Each fitting "extension" (I mean like, a 90 has two of these, a tee has three.) has a collar. You slip a brass sleeve over the pipe. The inside of the end of this sleeve is beveled nicely and this bevel is toward the fitting. You then expand the pipe, but not this brass sleeve and slip the pipe over the fitting. Then you use a tool with 2 U shaped heads to squeeze the sleeve over the pipe, onto the fitting. That is where that collar comes into play.
It takes a bit more time but for the discriminating plumber there is no better fitting system. Unfortunately, the fittings are not available in my area. Makes me sad.
A like new set of the Rehau tools for this system recently sold on eBay for over $800.00 so the tools are not cheap.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370068327317