In Excel, posted to GitHub. Right now I have:
- A real growth vs. nominal growth vs. inflation spreadsheet
- A Keynesian Cross spreadsheet; and
- A Production Possibility Frontier spreadsheet.
All of them are built on a minimal data entry paradigm; for instance, for the Keynesian Cross, you only need enter autonomous consumption, marginal propensity to consume, and intended investment, and the whole kit and caboodle recalculates from there. For the PPF, you just enter a maximum number of units, and everything recalculates: great for showing a collapsing or expanding PPF.