From the blog "Sandbox Update Notes"

+ Added Chests + Added Lava + Added Hammer - Primary tool for building, will replace direct building entirely in the future + Added Lemon + Added Dirt + Added Stone + Added Wood + Added /setspawn command (not yet functional) + Added interaction hints - used to display useful hints next to cursor when highlighting over certain objects + Added footstep sounds for most tiles + Added rain sounds + Added underground world type, with several world features + Added several playe