Franco-Prussian War (FPW) is an early SPI operational game by Jim Dunnigan that takes fog-of-war seriously. As with all double-blind wargames, starting with Avalon Hill Midway in 1964, there is a certain amount of trust required of each player to not break the game system by lying about hidden units. VASSAL easily accommodates double-blind games without the need of a referee.
The map is a scan of the original from an SPI games repository that came to light after vassalengine.org announced that they will start hosting SPI/DG modules. It has been cleaned up in GIMP and adapted somewhat for use in VASSAL.
The counters are vassal Game-Piece images that mimic the look of the printed counter set - except that the module ignores the historical designations printed on the counters because they are not necessary for game play. The rules refer to individual units simply by their combat values ("French 10"), so the module has separate generic game pieces for each size combat unit.
Step reduction is handled by a game-piece layer (where the original game used substitute counters).
In the FPW Standard Game, every combat unit and dummy unit is required to carry a separate marker indicating its formation: either Concentrated (having no ZOC, but full combat value) or Dispersed (has a ZOC, but fights at half strength).
The vassal module shows formation with a game-piece layer. Here we assume that all units are Dispersed unless specifically marked as Concentrated. This is shown as a rounded rectangle overlay on the game piece. When a player is challenged to reveal a unit's formation (by an enemy movement probe) he simply states the unit's status. Here's where the honor system kicks in, as it does when revealing whether a unit is a dummy or not.
In order to play the module, you will need your own copy of the rules, terrain effects chart, and the combat results tables.