The American Civil War is often referred to as the "first modern war."  Things like the telegraph and railroad were used to great effect.  There was also a lot of experimentation taking place on both sides.  The Battle of Seven Pines / Fair Oaks was the test bed for many of them.  Below are some of the special weapons that are included in The Devil's Own Fun.
This is the Agar Gun, also called the Coffee Mill Gun because of the hopper that fed the rounds.  This weapon was issued to several NJ regiments.  It was the first machine gun taken into battle.  It was capable of 120 rounds / minute and was gravity fed via a hopper.  In game turns, it will not have its own firepower, but will shift the results of the unit firing it.  It will also come with some significant downsides in terms of transport.
Not to be outdone, the Confederates developed a breech-loading, rapid fire weapon that shot a 1-lb projectile 2000 yards (max) at a rate of fire of 60+ rounds per minute.  In total, 40 of these were produced by the Tredegar Iron Works.  Seven different batteries received these weapons.  The Williams gun was first used as a weapon attached to Pickett's brigade.  It was modestly successful.  It made an impression, as over a year later, captured Confederate soldiers from Pickett's Division were asked about the rapid-fire weapon that made such a strange noise as it passed by.  In game terms, this is just another artillery battery with its own line on the weapons table.
Early in the war, "Professor" Thaddeus Lowe approached the Federal government with his plans for hydrogen balloons.  After winning a competition among him and several other designers, the government approved the production of four balloons.  Lowe worked diligently to perfect his design, coming up with a field inflation system that relied on iron shavings and hydrochloric acid.  This too was successful as he was able to move his equipment up the peninsula with the rest of the Army.  In the game, Balloons improve spotting for artillery and increase the command radius of leaders.  In the full version of the Currier & Ives lithograph, the balloon is clearly visible.