Some UNIX systems are distributed without nroff. Your operating system vendor may sell nroff separately as part of a text formatting package that isn't included with the base operating system. Or your operating system vendor may not provide nroff at all, meaning that you'd need to buy it from a third-party vendor such as Elan or SoftQuad. For systems without nroff installed, manual pages are supplied in a formatted (cat) form so that users can still read them without nroff.
The problem arises when you want to install third-party packages, either commercial or public domain, which don't supply formatted versions of their documentation. You can try to weed through nroff source, but you'd be better off if you could get a working version of nroff.
|gnroff||The Free Software Foundation version of nroff, gnroff, is on the CD-ROM.|
|awf||Another alternative is awf, an awk-based version of nroff. awf doesn't provide anywhere near all the functionality of nroff, but it does a pretty good simulation, and it's a very clever idea.|
awf recognizes both man and ms macros. To use it, you need to supply the macro package on the command line (as you would for nroff):
awf -man cat.1