As JF already pointed out, Ed Teixeira has released the "final version" of Chain Reaction 3.0, a free game based on the reaction system used in other Two Hour Wargame products. By the way, it has been reorganized like the more recent books (such as 5150 Star Army) making it easier to learn and to find information in it.
When the announcement was made on the discussion group, I learned that the first version of the game, released in 2002 as "Guns and Girls," was also available for the subscribers of the group. Reading through "Guns and Girls" it was possible to see how the system has evolved in the ten years since its first release. Many of the core ideas were already there, but a lot of streamlining (in a good way) has taken place to make the game more fluid and coherent. At the end of the book there are rules for a "wasteland campaign game," which made me even more eager to see the release of After the Horsemen.
Being in the miniature wargaming hobby for about one year, and playing mostly solo, I have found the Two Hour Wargames titles to be steady companions. For some people, it may take too much control away from the player's hand but for me the result tends to be amusing and unpredictable conflicts. I intend to play and post some games using Chain Reaction (maybe a small campaign) to celebrate its 10 year anniversary.