Available Modifications
Listed below are modifications that advanced users may choose to implement into the rendering of Overviewer. These mods may include additional information overlays into the output, the style in which tiles are rendered, or additional actions that are performed by Overviewer on each run. These typically require the administrator to have a little more knowledge of programming languages... as a note to developers of these mods, please feel free to update this list with links to your own scripts and mods.
Minecraft-Player-Locations https://github.com/ArchmageInc/minecraft-player-locations - A way to display current player locations in Minecraft on a rendered Overviewer map. Works for Minecraft 1.13 and above and uses RCON and a NodeJS server. 1.13 and below fix also available through minor hack.
PlayerMarkers https://github.com/overviewer/Minecraft-Overviewer-Addons/tree/master/PlayerMarkers - A bukkit plugin and Overviewer javascript file to show in-game player positions live on the rendered Overviewer map. Multiworld compatible and supports either MapMarkers or PlayerMarkers bukkit plugins.
Live Overviewer https://github.com/r15ch13/live-minecraft-overviewer - Showing in-game player positions live on the rendered Overviewer map now compatible with Sponge. Inspired by PlayerMarkers and utilizing Valandur/Web-API.
(may not work with Overviewer 0.9+)
Minecraft Sundial https://github.com/sunkid/minecraft-sundial/ - Will show your in-game server time as an overlay onto the Overviewer Map.
WorldGuard2OverviewerRegion https://github.com/overviewer/Minecraft-Overviewer-Addons/tree/master/WG2OvR - This PHP script takes the regions defined in WorldGuard, and outputs them in isometric cubes on your Overviewer map.
MCWeather https://github.com/overviewer/Minecraft-Overviewer-Addons/tree/master/mcweather - Add a current weather and forecast icon to your Overviewer map.
Menus http://code.google.com/p/overviewer-menus/ - Allows other addon developers to create simple menus.
WarpMarkers http://dev.bukkit.org/server-mods/warpmarkers/ https://github.com/deadcyclo/WarpMarkers - Shows /warp-points from Essentials on the map. Includes created by, time, last used by and time. Also shows /warp-points alerts (created, deleted, used).
Online Players Add a list of clickable links that displays players online. Updated for build June 20th build.
Base code by pironic & ethzero of GitHub, I simply updated it and moved the styling to the overviewer.css
https://github.com/KariTrace/Overviewer-Players-Online-Update