tools, such as 4th generation programming languages used for rapid prototyping to complex integrated CASE tools. 4th generation visual programming languages like Visual Basic and ColdFusion are frequently used since they are cheap, well known and relatively easy and fast to use. CASE tools, supporting requirements analysis, like the Requirements Engineering Environment (see below) are often developed or selected by the military or large organizations. Object oriented tools are also being developed like LYMB from the GE Research and Development Center. Users may prototype elements of an application themselves in a spreadsheet. As web-based applications continue to grow in popularity, so too, have the tools for prototyping such applications. Frameworks such as Bootstrap, Foundation, and AngularJS provide the tools necessary to quickly structure a proof of concept. These frameworks typically consist of a set of controls, interactions, and design guidelines that enable developers to quickly prototype web applications. Screen generators, design tools, and software factories Screen generating programs are also commonly used and they enable prototypers to show user's systems that do not function, but show what the screens may look like. Developing Human Computer Interfaces can sometimes be the critical part of the development effort, since to the users the interface essentially is the system. Software factories can generate code by combining ready-to-use modular components. This makes them ideal for prototyping applications, since this approach can quickly deliver programs with the desired behaviour, with a minimal amount of manual coding. Application definition or simulation software A new class of software called Application definition or simulation software enables users to rapidly build lightweight, animated simulations of another computer program, without writing code. Application simulation software allows both technical and non-technical users to experience, test, collaborate and validate the simulated program, and provides reports such as annotations, screenshot and schematics. As a solution specification technique, Application Simulation falls between low-risk, but limited, text or drawing-based mock-ups (or wireframes) sometimes called paper-based prototyping, and time-consuming, high-risk code-based prototypes, allowing software professionals to validate requirements and design choices early on, before development begins. In doing so, the risks and costs associated with software implementations can be dramatically reduced. To simulate applications one can also use software that simulates real-world software programs for computer-based training, demonstration, and customer support, such as screencasting software as those areas are closely related. Requirements Engineering Environment "The Requirements Engineering Environment (REE), under development at Rome Laboratory since 1985,