eSim was developed by Draper-Houston to provide a distributed analysis and simulation capability. It is a concept and architecture for Web-enabled simulation. It utilizes a Client/Server construct to Web-enable any simulation. First generation eSim is a general purpose simulation server. With eSim, any simulation can be executed, input parameters entered, and results viewed either in text format, graphically or via animation from a standard Web browser. Additional software and modifications to existing simulations are not required. eSim<SUP>i</SUP> provides an interactive capability which allows changing input parameters and viewing corresponding results during the simulation. It also provides the capability to run the simulation in real-time mode. Examples are used to illustrate eSim and eSim<SUP>i</SUP> capabilities.