I have also programmed Spigot plugins. These modifications run server-side and require no changes to the client to be enjoyed. I have a lot of experience developing plugins and I have done a lot free-lance work in the Spigot community. Occasionally however, I program something and release it public. These unique plugins are listed below.
WelcomePro is a bukkit plugin that displays a fancy welcome message when a player joins your server. In addition to the welcome message the plugin includes a more practical use because it also displays a configurable Message of the Day. Future plans include allowing the message of the day and the welcome message to be viewed by different groups or set differently for each group.
CustomBanMessage allows you to set a custom message that is displayed to a player when they are banned. The message is fully configurable in the config and this plugin is compatible with any banning system based on the Minecraft one (including Essentials). This is handy if you want players to know where they can appeal their ban or display other information.
InventoryGames is a plugin with a goal to allow players to play different games inside their inventory screen. Right now only one game is supported 2048. I will be updating this plugin frequently with bug fixes (if any are reported) and new features, and eventually other games.
UltimateBackpacks is a fully customizable backpacks plugin. Backpacks are chests that can be right clicked from the hotbar to be opened. This plugin could be useful for factions, prison, survival and many other gamemodes.