Metabolite-enzyme model
With a mean timestep of just 250ms, the metabolite-enzyme (ME) model is a simple, slightly stiff, generic model of 4 species — two metabolites, X and Y, whose production is controlled by corresponding enzymes, EX and EY — with 9 reaction channels.
This model was chosen because it is a small system, easy to work with in development, but stiff enough that reaction ordering matters somewhat. It has also been solved with high-resolution methods, so that good comparisons are available.