From project's WWW page:

ViewCVS: Viewing CVS Repositories

ViewCVS can browse directories, change logs, and specific revisions of
files. It can display diffs between versions and show selections of files
based on tags or branches. 

Additional features over cvsweb:
  * Template support: you can now customize the look and feel of ViewCVS
    by editing the provided EZT templates, which are used to generate the 
    pages.
  * Internationalization support: ViewCVS will parse and handle the
    Accept-Language request header, and can select different inputs for
    localized page generation.
  * Colorization for many file types via enscript.
  * Bonsai-like query features. (Requires MySQL and some other prerequisites)
  * Annotation/blame viewing support against a read-only repository.
  * Configuration on a per-virtual-host basis. This allows you to
    share the configuration file and ViewCVS installation across virtual hosts,
    yet still be able to fine-tune the options when necessary.

... and more!