From Second Life Wiki
|Important: Unless specifically called out in the associated blog post or on the Support Downloads page, all Second Life Viewers released to Residents whether Alpha, Project, Beta, RC, or Release, will connect to the main, LIVE Second Life Grid. If you elect to use one, be aware that all user information, as well as all L$, content, land, and other transactions are REAL.|
Linden Lab provides the following types of Viewers:
Second Life Release
A Second Life Release is the final, official release of a Viewer. Once released, the official Second Life Release becomes the default download for all new Residents. This is the most thoroughly tested Viewer available at any given time.
Second Life Release Candidate
A Second Life Release Candidate or RC Viewer is one built from a closely controlled code line. Only a Viewer believed to be very close to the quality desired in an official Second Life Release will be released as a Second Life Release Candidate. These builds are recommended for all Residents.
Second Life Beta Viewer
A Second Life Beta Viewer, which may still contain obvious bugs, is built from code that has been moved from rapidly changing development branches into code lines under a greater level of oversight and control. A Second Life Beta Viewer includes bug fixes, and possibly features, that are not yet available in the official Second Life Release.
Second Life Project Viewer
A Second Life Project Viewer is an early release from a Viewer development team to provide a preview of one or more new features. At any given time, there may be more than one Second Life Project Viewer available from different development teams. Most Second Life Project Viewer releases will be announced on the Technology Blog Channel, and represent the first opportunity to try new features and provide feedback to developers. Some of these Viewers will default to connecting to test grids rather than the main Second Life grid (see specifics in the announcement of each Second Life Project Viewer).
Second Life Development
Approximately every two weeks, the Snowstorm Project publishes a Development build; these builds are the latest collection of features under development for the next Beta release, but have not yet been through comprehensive testing. As a result, some bugs (possibly including ones that will result in inventory loss or other serious errors) may not yet have been detected and corrected.
Residents who wish to experiment with new features, actively log and comment on issues in the issue tracking system, and work with Linden Lab and open source developers to detect bugs and refine features are encouraged to try these builds.
Alpha or Nightly Viewers
Viewers referred to as Alpha or Nightly are Second Life Development Viewers built from the continuous integration system. New versions of these types of Viewers may be posted up to several times per day.
For information about the Linden Lab support policy, as well as a list of the currently supported Second Life Viewers, see Supported Viewers.