18GA

General Information

Here are some highlights of rules in 18GA:

Trains count towns for revenue but not for distance. (§4.2.3)
Montgomery and Talahassee is tokened by neutral corporation. That means they do not block tracing through them. See implementation notes below. (§4.2.3 i)
During Phase 2 and 3 corporations can only buy one train per OR from the bank. (§4.2.5 f)
Besides bankruptcy and bank broken, the game can also end if any corporation's market value reach $300. In case of bank broken or market value max the game ends in the current OR. (§5)
Privates Lexington Terminal and Waycon & Southern does not block any hexes. (Table III)

Augusta and Savannah starts as normal cities, but when a yellow city tile is laid there a label (Aug for Augusta, S for Savannah) are added to the tile. Further tile upgrades in those city must use the specific tiles.
Brunswick and Macon starts as normal cities, but when they are upgraded to green cities a label (B for Brunswick, M for Macon) are added to the tile. Upgrading to brown can only be done with their specific tiles.
Montgomery and Talahassee appear as cities, with a neutral token, in the 18xx.games implementation. On physical maps they appear as towns, but the rules do specify that they are cities for train distance purposes, so the final result is the same.