You're probably aware of the various types of artillery throughout history, such as the ballista, scorpion, onager, trebuchet, just as varieties of catapults for starters. The ballista and scorpion are virtually the same basic design even, except the scorpion was smaller and more suited to a purely anti-infantry role whereas the ballista was more powerful and could be used to take out siege towers or send a single spear through a column of infantry. Onagers hurled clusters of rocks and was, basically, a siege shotgun of the medieval era. The trebuchet was unique in that it used the potential energy of a counterweight to power whatever projectile was placed into the sling, and the largest trebuchets were even able to ablatively wear away a castle wall.

Closer to the modern era, there have been so many varieties of cannons and firearms made - each with their own unique advantages and disadvantages. They could all be considered the same basic weapon, cannons and firearms, since both use a pressure wave to propel a kinetic energy projectile, but that would be, in my opinion, to not recognize the wider variety amongst the different types but instead to consider them equivalent on the basis of similar operation (or method of downrange effect). I see it this way, each have their own strengths and weaknesses compared to one another; even if two weapons/ships operate by similar principles. or have similar methods of affecting the enemy target, other factors - such as rate of fire, damage points, area of effect, accuracy, range, crew compliment, health, etc - allow for various applications to be performed by each.