ProjectileTrajectory is a plugin for the bukkit API for Minecraft Servers.
ProjectileTrajectory allows you to draw the trajectory of projectiles like snowballs or eggs. For example: If you want to calculate the trajectory of a snowball, you just have to hold it in your hand and the trajectory will be rendered using particles. It is possible to select certain particles for every type of projectile, e.g. green sparks for potions and hearts for snowballs..