Sponge is a combination of a new API  most likely based off of Spout and Flow’s APIs  on top of Forge, with assistance from other parts of Minecraft’s modding community (Glowstone, Canary, etc.). 

Popular Members/Teams that are Contributing

• sk89q (of WorldEdit/WorldGuard) - project lead
  
•  blood (of MCPC+/Cauldron) - project lead 
  
• LexManos (of Forge/FML/MCP)
  
• cpw (of Forge/FML/MCP) 
  
  
• Portions of the Spout team (Zidane/Raphfrk/DDoS/Sleaker/Owexz/Wulfspider) 
  
  
• Portions of the Flow team (kitskub) 
  
  
• Portions from ForgeEssentials (AbrarSyed) 
  
• Other Bukkit Plugin developers (KHobbits/Elgarl/zml) 
  
• Portions of the FTB team 
  
  
• The Canary team 
  
  
• Glowstone (SpaceManiac) 
  
  
• Portions of the XereoNet squad 
  
  
• Spigot team 
  
  
• Some previous contributors to Bukkit 
  
  
• ANYONE  CAN JOIN AND HELP!
  

Benifits of having a Community ran API:
We get to choose what is put in future updates. 

Information:
Sponge will be created using already known Minecraft Code. It will utilize Java 1.6 and Spout API.  It will be made to match Bukkit to the best of its ability, while watching copyright. Sponge will be licensed under MIT, Sponge doesn't have a Official release date, anyone can Apply for developer on the Sponge website,Sponge will both run Mods and Plugins.

This is only a little information about Sponge read more from the link below:

Sponge Website: http://www.spongepowered.org