"Incendiary bolt launcher. Starts fires."
An incendiary launcher is a single-shot rifle that fires an explosive incendiary bolt. The bolt will explode into flames and pawns and anything flammable in the target and adjacent squares will catch fire. An incendiary launcher can be a very potent weapon as it can effectively disable enemies as they run around engulfed in flames, and therefore a potential big threat if you don't properly micromanage enemies with incendiary launchers or prioritize them soon enough. Incendiary launchers do appear to become less common later in the game as enemies favor powerful weapons such as charge rifles, triple rocket launchers, and grenades. An incendiary launcher can trivially dispose of infestations (which can become very problematic if left uncontrolled or with higher colony wealth on higher difficulties).
Its low base damage is compensated by the damage over time of the fire if not put out quickly. It's effective against wildlife since it burns large areas, affecting many animals at once, unless extinguished by rain.
The projectiles launched will not account for movement of targets. This can be an advantage when facing them as one can move out of the way, but it can be a disadvantage when firing at fleeing enemies because they're moving. One can also have a colonist run around one with an incendiary launcher and shoot the running colonist. The runner will outrun the projectiles, starting wildfires, useful for clearing out areas to prevent larger fires.