Rules for playing Stargrunt II in different time periods or in different science fiction mileus.
Hardtack - American Civil War rules for Stargrunt II. This is an extensive variant that includes rules for mounted troops, formations, different types of artillery shells, and far more. This can be used for historical Civil War games, or it can be used in Guns of the South style science fiction time travel scenarios. It would be easy to expand it for any 19th Century scenarios.
Standards of Valor - Phil Pournelle's excellent rules for Dark Ages games based on Stargrunt II. Available as a Word document download.
Traveller - some thoughts for converting Stargrunt II to Marc Miller's Traveller universe.