I am not overly familiar with the Hussite Wars, as there doesn't seem to be a great deal of English scholarship on it. The use of wagon forts is not entirely unprecedented in medieval warfare. Edward III seems to have created one out of his baggage trains before the Battle of Crecy in order to protect the rear of his army. There are even some accounts which claim he mounted artillery on some of the carts, although these are viewed with skepticism. Edward's wagon train is quite different from the ones Hussites constructed. The bulk of his army was well in front of them and any artillery that may have been present did not have a major impact on the battle. The idea for Edward's wagon fort may have evolved from the need to enclose the horses of the English army, which fought dismounted. To my knowledge, the wagon fort tactic was never used by the English again during the Hundred Years War. However, they did use plenty of defensive structures to protect their footsoldiers and archers against cavalry charges. These ranged from trenches to cut brush to pointed stakes. While the Hussites seem to be fairly unique in their use of the wagon fort, they are not the first medieval army to have developed sophisticated defenses against cavalry charges. The utility of a wagon fort would be minimal in an era before gunpowder artillery, as weapons like catapults and springalds were not commonly seen in field engagements. It may also be the case that the Hussites had more wagons to spare in creating a fort, while previous armies had less available to them. The number of wagons utilized by medieval armies increased over the 15th century as gunpowder artillery required larger and larger logistical trains.