SCToolkit (Scientist's Component Toolkit) is an experimental app for constructing simple math, science, and educational applications using a small set of pre-defined components that inter-operate in a standard way, and data objects (currently 0, 1, and 2-dimensional numerical values) that flow between these components. Described this way, SCToolkit resembles one of the many "box-and-wire" software construction sets that have been available for many years on other platforms. SCToolkit currently contains 10 built-in components for creating and reading data, performing math and other operations on data, displaying and saving results, and for acquiring user input and interaction. 15 examples are provided which can be used as templates for other "data-flow diagrams", or diagrams can be constructed from scratch using the palette of components. An extensive help section is also provided in the app, explaining the use of diagrams, components, and the examples. Data and diagrams can be shared via iTunes. The companion website provides additional information, a copy of all the help, and examples submitted by other users. Future versions of the app will include new built-in components for specific data input, processing, display, and output functions which have been requested by users. This app works best on the iPad 2 or later.