The group or meeting simulation is one of the easiest to develop. Without prop or costume, the group simulates some activity. Simulations that use this approach simply ask the group (typically a school class) to pretend to be something they are not and act as they believe that group would act. Simulations of this type are actually common in classrooms. You've probably seen or heard about classes pretending to be the Continental Congress, performing in a mock trial, or pretending to be a group of Oregon Trail travelers meeting around the campfire.
At the simplest level, you just do it. Of course, preparation of the group enhances the simulation. Before you can pretend to be a member of the Continental Congress, it helps to know a little - if not a lot - about the Continental Congress. If you know who was there, you can have members of the group portray individual characters. It's a fine thing to write a report about Edmund Rudolph of Virginia who wrote out the first draft of the new Constitution, but it's much more significant educationally if you use that information to more accurately portray him in a simulation of the Continental Congress. When you write a report about Edmund Rudolph or anybody else, you learn something. When you portray Edmund Rudolph or anybody else, you remember it forever.
Mock trials are a good example of a simple simulation using a group. The law firm of Anderson Kill & Olick, P.C. does a mock trial related to the sinking of the Titanic for sons and daughters of their employees. They provide a complete set of information and hold a simulated trial so that sons and daughters can see the legal process at work in an interesting manner. Their web site at http://www.andersonkill.com/titanic/home.htm provides plenty of great information. They don't show pictures of their trial, but even without costumes, it would be an interesting way to teach via simulation. Not only would you learn about the trial process, but you'd learn about the Titanic tragedy as well.
Of course, many legal firms hold simulated trials in order to prepare defendants for questioning and increase comfort levels of attorneys. There are even companies that specialize in preparing legal firms for trials via simulated legal proceedings.
Various states hold mock trials. One such program, co-sponsored by the Connecticut bar association, provides high school and middle school students with the experiences of a mock trial. More information is available at their web site: http://www.connix.com/~cclce/programs.html
Yet another example is the model United Nations. A group can simulate the activities of this organization simply and easily. Preparation is important, perhaps, but props can be minimal. More information is available on the U.N. website at http://www.un.org