When a player joins the server, other players have a configurable period of time where saying any message that includes "welcome back" or "wb" (capitalization doesn't matter) will trigger an event that gives them a random (configurable) item as a reward. It is a simple plugin to reward players for being nice to each other. In the config, you can set the list of items the plugin chooses, their relative chances, the welcome time window, and the cooldown period (prevents players from spamming join and leave to farm items).