Kill Rewards is a plugin that executes a configurable command whenever a player reaches a certain number of kills, or kill streak. It is designed to exclude bloatware, and to be easily configurable.
Upon first installation of the plugin, a config.yml file will be created in the plugins/KillRewards directory. The file consists of a single list node kill_rewards, which contains the list of kill rewards you want registered on the server. Each kill reward node comprises of two separate nodes: the conditions, and the command. Conditions specify when the reward should be given to a player (they are evaluated when the player gets a kill). The command is executed when the conditions are met. This is where you would want to add the 'reward' part. Instead of rewarding the player, you can also use the plugin to broadcast a player's killstreaks at intervals, inform a player of the number of kills they have every time they get a kill, etc. More information on how conditions are structured are provided within the config file itself.