Have a cool server, but wish more people could see it from the comfort of their web browser? WebSandboxMC allows modern web browsers to view and interact with a small part of your server's world using WebGL and HTML5 technologies:

Currently supports:

Exposes a small piece of your server to web users, with configurable location and dimensions
Web users can place/break blocks, and see server block changes in realtime
Web users can send/receive chat, and other users can see their chat messages
Web users can see players on your server and other web users move and rotate
Sheep are spawned with custom names and track the web users movements

WebSandboxMC embeds a copy of NetCraft, online demo: https://satoshinm.github.io/NetCraft/ (you can connect to a WebSandboxMC server by typing /online servername)

Official test servers: feel free to stop by and say hello! (chat is enabled)

http://netcraft.herokuapp.com (slow, temporary) - Note: if no one is currently online, the server will take a few minutes to startup! This test server is web-only, and is not persisted to disk.
~~(offline) https://netcraft.beerprojects.com~~ ~~- new (2017/05/29) faster test server, Minecraft client connections enabled, as well as ThinkMap and Dynmap! (config source)~~

Once the plugin is installed, visit the URL printed in the server log on startup to load the client and automatically connect to your server.

Release downloads: https://github.com/satoshinm/WebSandboxMC/releases (also available at Spigot Resources: https://www.spigotmc.org/resources/websandboxmc.39415/)
Documentation/source: https://github.com/satoshinm/WebSandboxMC
Issue tracker: https://github.com/satoshinm/WebSandboxMC/issues

Disclaimer: This plugin is early in development, there may be bugs and/or missing features. Use at your own risk, but high-quality issue reports and code contributions very welcome.