Just in case you missed my Twitter post, Two Hour Wargames have released an updated version of their Chain Reaction rules incorporating all the latest mechanics from their main rule sets.
And they're letting you download it for free!
Of course it doesn't have all the bells and whistles (and particularly the period specific campaign rules) of the their other sets (Nuts!, FNG etc.) but it's a great way to take a look at their excellent reaction mechanics.
You can find it available for download at http://www.angelfire.com/az3/twohourwargames/CR3.0.htm