There are alternate viewers to use for Second Life, mostly third-party viewers which have been created by resident developers not working for Linden Lab. Third-party viewers are no way associated with Linden Lab. All viewers are free to download and install.
The link above lists the most popular viewers to use for Second Life, including details of the different viewers, top features it offers, futher links for more information and displays the latest versions. This wiki page is subject to change, so check by reqular for updates on the viewers.