There are some from what I can tell:
#1 is weapon options which are not universally accessible in the same numbers. and some special units available to various nations
#2 is national special rules:
Germany: German Officers get +1 order die to issue when giving an order to nearby troops; They get essentially a 2+ mission tactics if NCOs die(you get -1 morale if nco is dead), +1 RoF for LMGs/MMGs, PzIVs and big cats impose a -1 to enemy units' orders that aren't to shoot that vehicle.
Brits: Free artillery OP(about 100pt value) and they can still get the normal one allowed, Best of two results on prelim. Bombardments(mission special rule), And one of the following: auto-pass orders to assault, Defenders assaulted get no reaction to assault, roll +1 die per 3 men fighting in assault, roll +1 die per three men shooting, 4+ to lose a pin marker before rolling for order if enemy within 12"
USA: Rifles and BAR get no penalty to hit while moving, many tanks get no penalty to shoot with main gun while moving, Air Observers get to call 2 air attacks instead of 1, no -1 order penalty for units off table as reserves or like to arrive.
USSR: Reroll morale tests if the consequence would be to be destroyed, Free inexperienced rifle unit with any/all options(112pt value), if unit within 6" of commisar fails order roll, you must kill a guy and reroll, Artillery barrages roll 2d6(pick highest)+6 for radius instead on 1d6+6 for area of effect.
Italy: difference in # of units destroyed gives bonus or penalty to all orders, Reroll to defend in missions with an attacker and get bunch of advantages when defending,
Finland: When units get to 50% strength they upgrade quality(Inexperienced-Regulars, Regulars to Vets, Vets- Vets with +1 morale), When given ambush order(overwatch) can reroll morale, when shooting from ambush rifles get a +1 to hit modifier, Ignores -1 order for outflanking troops to arrive
Bulgaria: Can't be outflanked, Get to take one german or italian unit as support that isn't vet and can't be a heavy or superheavy tank.
Hungary: Get to take one german or italian unit as support that isn't vet and can't be a heavy or superheavy tank(as exception can take a tiger I), HQ units get the fanatic special rule
Romania: Get to take one german or italian unit as support that isn't vet and can't be a heavy or superheavy tank, get free AT gun or non-heavy arty at regular in addition to normal allowance of 1 (up to 110pt value).
Japan: Everybody gets Fanatic rule(basically fight to the death), Autopass orders to run/charge nearest enemy, If a unit gets to start game hidden it is also in ambush(overwatch), Political officers allow you to reroll result for any green(untested) units morale level after they take casualties within 6"
France: Greater chance opponent gets to act first on turn 1, Free non heavy arty or AT gun(up to 75pt value), buy 3 inexperienced infantry squads get a 4th for free that is same as cheapest one(theoretically up to 121pt value)
Belgium: Same as France except the inexperienced infantry unit has less options
Dutch: Same as France except the inexperienced infantry unit has less options
Norway: Greater chance opponent gets to act first on turn 1, Hidden units get to start with Ambush orders, unaffected by difficult terrain on turn 1, no -1 for outflanking troops to show up.
Poland: Greater chance opponent gets to act first on turn 1, Reroll morale tests if they would result in a unit being destroyed, Officers are Fanatics
Greeks: Same as Norway
Partisans: 3 Hidden bomb markers that probably do nothing when enemies get within 6"(1-3: no effect and goes away, 4,5: nothing yet, 6: counts as a heavy howitzer hit!) Hidden units get to start with Ambush orders, unaffected by difficult terrain on turn 1, no -1 for outflanking troops to show up. Can take a captured tank must be inexperienced biggest available is a panther.
I think this is all the factions