Scilab is a numerical computational package developed by INRIA and École nationale des ponts et chaussées (ENPC) in France. It is a high level programming language, most of its functionality based around it being easy to condense many single computations into one line of code. It does this primarily by abstracting primitive data types to be functionally equivalent to matrices.
It is similar in functionality to MATLAB and is available to download at no cost. The program enables users to compute a wide range of mathematical operations from relatively simple operations such as multiplication to high level operations such as correlation and complex arithmetic. The software is often used for signal processing, statistical analysis, image enhancement, fluid dynamics simulations etc.
The Scilab web page describes it as "open source" software. However, since its license does not permit commercial redistribution of modified versions, it does not satisfy the Open Source Definition and seems to belong to the semi-free software category.
Scilab has been widely used in several industry and research projects, and many contributions have been made by users. The syntax is similar to MATLAB but the two are not completely compatible, though there is a converter included in Scilab for MATLAB=>Scilab Conversions. Scilab has fewer help files than MATLAB.
Scilab also includes a package called Scicos for modeling and simulation of explicit and implicit dynamical systems including both continuous and discrete sub-systems and the screenshot shows the Scicos block diagram editor in the top right window.

Syntax
Scilab syntax is largely based on the MATLAB language. The simplest way to execute scilab code is to type it in at the prompt, >> , in the graphical command window. In this way, Scilab can be used as an interactive mathematical shell.