Display of players, tps and memory in the web
SimpleTickets is a easy ingame ticket system that should help to manage any amount of support needing players.
DKE Developer's help pages plugin.
Advanced player tracker using the ScoreBoard api
A plugin developer tool to allow you to create custom popup menu systems for vanilla minecraft players using an API
A plugin in which the user can create Daleks from Doctor Who
UHC Chunk Preloader is a plugin that will generate the chunks in your world before you start playing.
OPDS enables a detection if a player is online or offline and triggers a redstone signal.