When OpenSimulator first appeared in 2007, its ambition was to create an open-source platform capable of running virtual worlds that were compatible with the Second Life viewer. In its early years, the similarities between the two platforms were striking. Regions looked familiar, avatars behaved in much the same way and content could often be transferred between compatible grids. However, as both projects matured, they gradually diverged, each pursuing different goals and priorities.
Second Life has always been developed by Linden Lab as a commercial platform. Every aspect of the software is tightly controlled, allowing the company to introduce new features while maintaining consistency across the entire grid. OpenSim, by contrast, is an open-source project maintained by volunteers and independent developers around the world. Rather than supporting a single virtual world, OpenSim provides the software that anyone can use to create their own grid or standalone simulator.
This difference in philosophy has led to significant technical divergence over the years. Linden Lab has invested heavily in technologies such as Physically Based Rendering (PBR), Experience Tools, Animesh, environmental enhancements, improved avatar systems and server-side optimisations. OpenSim has adopted many similar features where practical, but its development has often focused on flexibility and compatibility rather than reproducing every Second Life capability.
Perhaps the greatest difference between the two platforms lies beneath the surface in their physics engines. Second Life licenses the Havok Physics Engine, one of the most respected commercial physics systems in the gaming industry. Havok is used by numerous AAA games because it delivers highly accurate collision detection, stable object interactions, realistic vehicle handling and reliable physical simulations even in demanding environments.
The Havok licence comes at a considerable cost, making it impractical for an open-source project such as OpenSim. In addition to the financial implications, Havok is proprietary software and cannot simply be incorporated into an open-source application without licensing agreements. As a result, OpenSim has always relied on freely available physics engines instead.
The earliest versions of OpenSim commonly used ODE, the Open Dynamics Engine. ODE provided the basic physics needed for walking avatars, moving objects and simple vehicles, but it was never intended to compete directly with Havok. While perfectly adequate for many everyday tasks, ODE often struggled with complex collisions, stacked physical objects, realistic vehicle behaviour and high-speed simulations. Many OpenSim residents became familiar with vehicles bouncing unexpectedly, boats behaving unpredictably or objects occasionally passing through each other.
In later years, many OpenSim grids adopted BulletSim, a physics engine based on the open-source Bullet Physics library. BulletSim represented a considerable improvement over ODE, offering more stable collisions, smoother vehicle movement and better handling of complex physical interactions. For many region owners it became the preferred choice, particularly for roleplay regions, driving environments and sailing communities where reliable physics were especially important.
Despite these improvements, BulletSim still cannot fully replicate Havok. Havok has benefited from decades of commercial development, optimisation and testing across countless games and simulation projects. Its collision detection is more sophisticated, object stacking is more stable and physical interactions generally feel smoother and more predictable. Vehicles in Second Life tend to respond more consistently to changing terrain and collisions, while physical objects are less likely to exhibit the unexpected behaviour that can occasionally occur in OpenSim.
This difference is particularly noticeable when creating advanced scripted vehicles. Cars, motorcycles, aircraft and boats can certainly be built in OpenSim, and many perform extremely well with careful scripting. However, creators frequently need to design around the limitations of the available physics engine, using additional scripting techniques to compensate for behaviour that Havok handles more naturally. A vehicle that performs perfectly in Second Life may require significant adjustment before it behaves satisfactorily in OpenSim.
The divergence has also influenced content creation. Because Second Life offers a single, standardised environment, creators know exactly which physics engine, simulator version and feature set their products will encounter. OpenSim, however, exists as hundreds of independent grids, each potentially running different simulator versions, physics engines and configuration settings. Content creators therefore often need to test their work across multiple environments to achieve consistent results.
None of this should be seen as a criticism of OpenSim. The project has achieved remarkable success using entirely open-source technology and volunteer development. It provides freedoms that Second Life cannot, including the ability to host private grids, customise simulator behaviour, alter source code and create enormous virtual worlds connected through the Hypergrid. These advantages have attracted educators, researchers, hobbyists and independent communities from around the world.
Nevertheless, the absence of the Havok Physics Engine remains one of the principal reasons why OpenSim physics can never completely match the experience found in Second Life. Unless Havok were ever to become freely available or an open-source physics engine were developed that could equal its capabilities, this gap is likely to remain. BulletSim continues to improve and provides excellent performance for most applications, but the precision, stability and maturity of Havok still give Second Life a measurable advantage in complex physical simulation.
Today, Second Life and OpenSim have grown into two distinct platforms. Second Life continues to evolve as a commercially managed virtual world with cutting-edge technology and consistent performance, while OpenSim remains a flexible, community-driven platform that places freedom, openness and customisation above commercial constraints. Both have their strengths, but their different approaches to development and physics ensure that each offers a unique experience for residents and creators alike.
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