2004Scape is an open-source projected created by Pazaz with the goal to preserve Runescape as it was in, you guessed it, 2004. While there is currently a hosted server for all to access at 2004.lostcity.rs that's not the end goal. Currently the server is running a May 25, 2004 version of the game. With much help from all of the contributors all available archived cache files from the game will have a runnable version of the game.
So yeah, just like go check it out. The fun won't stop at 2004, in fact it's just the opposite! The masochists over at Lost City will continue developing this for as long as possible for updates going into 2005! 2006!! 2007!!! 2008?! 200...9?... and beyond!
But seriously, if you're into programming go checkout the repo and get creative with it or join the other contributors in preservering RuneScape.