EmTeX for PCs running MSDOS or OS/2, MikTeX and fpTeX for PCs running Windows and OzTeX for the Macintosh, all come with previewers that can be used on those platforms. EmTeX's previewer can also be run under Windows 3.1.
Commercial PC TeX packages (see commercial vendors) have good previewers for PCs running Windows, or for Macintoshes.
For Unix systems, there is one 'canonical' viewer, xdvi. Xdvik is a version of xdvi using the web2c libraries. Unix TeX distributions (such as teTeX or NTeX) include a version of xdvik using the same version of web2c as the rest of the distribution.
Alternatives to previewing include
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