opensim-SC is a fork of OpenSim, and OpenSim is a clean room fork of Second Life. They are all 3D virtual worlds that are open, users can create their own content, these are not games. Second Life is a proprietary server, with open source viewer. OpenSim is an open source server that works with Second Life viewers.
The SC in opensim-SC stands for SledjChisl, part of the SledjHamr project.
opensim-SC is part of the SledjHamr project. SledjHamr is a rewrite from scratch of Second Life (SL) / OpenSim (OS) style 3D online virtual world client / server. The plan is to use OS server and SL clients as crutches, when a bit of SledjHamr is ready, it replaces the matching bit in OS/SL.
While OpenSim is slowly morphing into SledjHamr, it needed a name, so I called it SledjChisl. The main differences between opensim-SC and OpenSim are listed in Differences.txt
It's a 3D open online shared virtual world that is user created. Using a specialised bit of software called a viewer you log onto one of these worlds, either Second Life, or one of the many OpenSim based worlds. You then get to wander around a 3D world that the other users have built, and do many things. Including building your own bit of the world using the viewer itself.
Many people think of it as a game, but it's missing many of the features of a real game, and tends to be more about the social side of things. I've even had someone tell me that everything online is a game, even pointing out that their bank account is online didn't help. There is no goal, no game play, no levelling up, no one keeps score. You do what you want in these worlds (within the limits of the local rules), and that might include playing games that people have created in the world, but you don't have to.
People even do business in them.
The easiest thing to do is to just join a world that is running opensim-SC, but you don't need this software for doing that. This software is for running such a world, or part of it.
Virtual world software is complex software, coz you are simulating an entire world. There's lots of things to take care of. While SledjHamr aims to make things as simple as possible for ordinary folk, we ain't there yet. opensim-SC is slightly easier to setup than OpenSim, so progress has been made. opensim-SC tries to remain compatible, so for more details, refer to the OpenSim and Second Life documentation.
You'll need to be familiar with command lines. Currently opensim-SC uses Linux shell scripts, though that'll change in the next release to be more portable to other operating systems. The shell scripts are for setup and basic management, the virtual world software itself is written in portable C# that runs on .NET and MONO.
The scripts install and manage everything based on a Debian variation of Linux, it's been tested under Debian, Devuan, and Ubuntu. Refer to INSTALL.md for installation details.
The scripts are documented here.
The new configuration setup and options are documented here.