As you may know, Classic is the earliest phase of Minecraft's development, lasting in 2009. Although not many classic versions are found, one is available in the launcher (last time I checked, at least), and that's c0.30_01. Unlike the original versions of classic that used to be on http://minecraft.net/classic/play.jsp and http://minecraft.net/play.jsp earlier, which have sadly been removed, the launcher version does not have server support. That is, until now. Many classic clients usually run on modified versions of c0.30_01, but ClassicCraft stands out from the crowd. We only modify the game to add features that no longer work such as the online mode, and multiplayer, not adding things that the game doesn't need. This is just Classic in its true form. There are two modes players will be able to play in: Online Mode and Launcher Mode. Online mode will let you play by using a web browser*, while Launcher mode will let you play in your own Minecraft launcher. There will also be a server. While this mod is not released yet, as we have some unfinished prototypes; Launcher mode will be coming sometime this Summer, while Online mode will come in Fall due to issues with logging in.
To stay up to date with updates, be sure to follow us on Twitter and check out the mod's repository on Github.