Simulate alternate OD&D disease mechanic
Dave Arneson added disease rules to Original D&D in Supplement II: Blackmoor. However, arguably they're a little clunky (mostly involves fixed calculator work once the disease sets in).
Here we have a simulator to test an alternate OED mechanic in which a save is rolled every day, and the victim takes Strength damage if failed. We used this to synch up the fatality rates with the original rules in OED Judges house rules 1.0.6.
For new diseases, you can edit the time units and damage incurred until you get the appropriate fatality rate.