What is BYOND you ask?

According to their own site, it's this:

"BYOND is 100% free, and is excellent" -- Richard Bartle, father of the MUD.

BYOND is the premier community for making and playing online multiplayer games. Enjoy hundreds of games created by our community, by people just like you. BYOND supports board and card games, role-playing, action, strategy, and more!
Right now, BYOND players are online exploring the worlds of fantasy RPGs, playing virtual trading card games, battling in action-packed multiplayer arenas, plotting to take over the universe in epic real-time strategy sims, and even enjoying friendly casual games like online chess. Free games are right at their fingertips.
Want to Make Games?
Making your own multiplayer games with BYOND is free. As a game creation system, BYOND is powerful and flexible, with an easy-to-learn language and tools for developers, plus articles and tutorials. Building multiplayer games is easy with built-in online support. Find out how easy it is to create the game of your dreams. Your game could be the next big indie games sensation!