Subversion repositories served with Apache have the nice built-in feature: the repositories can be browsed with any webbrowser at no additional cost.
For Subversion repositories served via svnserve, this is not possible because browsers don't understand that protocol.
The SVNProtocolHandler for Internet Explorer allows browsing svn:// urls from within the Internet Explorer. No need to install a Subversion client, just use IE. This also adds the benefit that you can click on svn:// links and quickly the URL you received from a colleague via email.
Note: the protocol handler only works in Internet Explorer. Firefox users either have to switch back to IE for svn browsing or hope someone will create an svn:// handler for them.
The installer for the SVNProtocolHandler can be found
on the download page.
Note: even though the SVNProtocolHandler is developed by Stefan Küng, it is not part of TortoiseSVN and won't be included in TortoiseSVN either. It will remain a separate download, and it has its own project page.