"OpenSim is the open source implementation of Second Life (but using .NET, alas); its existence is what makes the new Open Grid possible. Without the open source behind it, this would simply be a closed approach similar to old-style online services such as AOL or CompuServe. Linden Lab's decision to open up its protocols means that there is a chance to create a virtual world equivalent of the Internet, which anyone can use, and where anyone can contribute." (http://www.computerworlduk.com/toolbox/open-source/blogs/index.cfm?entryid=1095&blogid=14)
"OpenSimulator is an open source multi-platform, multi-user 3D application server. It can be used to create a virtual environment (or world) which can be accessed through a variety of clients, on multiple protocols. OpenSimulator allows virtual world developers to customize their worlds using the technologies they feel work best - we've designed the framework to be easily extensible. OpenSimulator is written in C#, running both on Windows over the .NET Framework and on Unix-like machines over the Mono framework. The source code is released under a BSD License, a commercially friendly license to embed OpenSimulator in products. If you want to know about our development history, see History.
Out of the box, OpenSimulator can be used to simulate virtual environments similar to Second Life™, given that it supports the core of SL's messaging protocol. As such, these virtual worlds can be accessed with the regular SL viewers. However, OpenSimulator is neither a clone of Second Life's server nor does it aim at becoming such a clone. On the contrary, OpenSimulator lacks support for many of the game-specific features of Second Life (on purpose), while pursuing innovative directions towards becoming the bare bones, but extensible, server of the 3D Web.
OpenSimulator is getting more stable as it approaches release 1.0, but we still consider it alpha software; so should you." (http://opensimulator.org/wiki/Main_Page)
"OpenSim was created with libsecondlife, an open source library derived from the source code to the Second Life's viewer. The code that operates SL's server grid remains closed source, however, so OpenSim is a fully open alternative.
As leading OpenSim developer Adam Frisby stated:
"We used the term 're-engineered'-- it was re-implemented from standards, but on the backend it's a very, very different beast. As best as we can tell (without seeing the source to the Linden Lab server), the structure internally is radically different partly due to our desire to keep things usable for non-SL style worlds."
OpenSim is the leading platform for 3D websites in a way that Apache is the leading platform for 2D websites.
Over two dozen on the OpenSim group's Grid List ( http://opensimulator.org/wiki/Grid_List) have emerged with many designed to serve specific groups and activities, such as for the Chinese market. Reactiongrid, an OpenSim area, is now running on SQL Server, Microsoft’s offering in the highly-competitive database market.
There are many veiwers for OpenSim including realXtend, The Hippo OpenSim viewer, - The Opensim Kid Browser and Xenki." (http://thefutureofartificialintelligence.blogspot.com/2008/09/ai-93-apache-platform-for-2d-websites.html)
- interview with OpenSim developer, Teravus Ousley, describes some of the work being done to create documented protocols that will make OpenSim fit seamlessly into Web 2.0 architecture