Linden Lab provides official viewers for Microsoft Windows 2000 / XP, Mac OS X, and most distributions of Linux. A third-party version is available for Solaris and OpenSolaris. Since the viewer is open source, users may recompile it to create their own custom viewers; modified viewer software is available from third parties. The most popular is the Nicholaz Edition; this viewer, produced by Nicholaz Beresford, includes bug fixes developed outside Linden Lab that are not yet included in the Linden Lab code. The Electric Sheep Company has introduced the OnRez Viewer, which makes substantial changes to the design of the user interface. ShoopedLife is a Second Life client that generates randomized hardware details and sends them to the Second Life server as part of the login, rendering the user anonymous, save for their IP address.

An independent project, libsecondlife, offers a function library for interacting with Second Life servers. libsecondlife has been used to create non-graphic third party viewers, including SLEEK, a text browser using.NET, and Ajaxlife, a text viewer that runs in a web browser.

In February  a partnership between Linden Lab and Vollee was announced. In May, Vollee launched an open Beta trial for a Second Life mobile application that lets Residents travel and communicate in-world by logging in from a handset using an existing account. The service, introduced for free, requires downloading a thin client to a 3G or Wi-Fi enabled handset.

A special beta client is available, which is updated very regularly, and is used for constant software testing by volunteers. The beta client connects to a "beta grid" which consists of a limited number of regions mirrored at regular intervals from the real grid. The mirroring process overwrites any changes made on the beta grid, and thus actions taken within it are not stored by the servers; it is for testing purposes only. Every few months, the standard software is replaced by the beta-grid software, intended as a big upgrade. The Second Life user-base is growing rapidly, and this has stimulated both social and technological changes to the world; the addition of new features also provides periodic boosts to the growth of the economy.