Slitherine

while it says the battle of France, for me it's the whole start of the way with different goals and outcomes from a slightly different plan held right from the start i'm interested in, so not to repeat history but make your own, or not, which ever the outcome

so a game engine to use?

then some idea's on plans to use, yes your the allies and for starters and sake of argument, the Germans use the history plan and work around it once altered by the allies not doing as planned.

Maginot Line built, manned and totally finished.

German invasion of Poland starts, and on day one then a counter attack by the French and Belgium forces on 2 fronts which soon halts the Germans with the help of the Poles which opens a 3rd, Luxembourg and the Netherlands join in with sending advanced units while the British Expeditionary Force (BEF) lands a few days later and joins in, so no Phoney War and Australia, New Zealand, South Africa and Canada send troops to reach the Allies asap.

so the German strategy / plans fails at the first hurdle then falls altogether to pieces and goes onto the defensive to hold until more units arrive to muster a new plan on a larger wide multi front.