MisterFiber - Original developer, concept.
ScottKillen - Saviour of original mod, master coder, technical support, buddy.
JLBShecky - Lead developer.
allaryin - Other lead developer.

Shout out to:
asie - Significant help with the port from 1.6 to 1.7
TDWP_FTW - Some graphics, many ideas, blocks, some biomes.
BlacksWhites - Idea for Wasteland.
MindKrafter - Idea for Marsh.
Exalm - Continuing development of the original ExtraBiomes.
HarpSeal - Cool guy.
toughenough6 - First post on original topic.
paull105 (AKA, SirDerpingtons) - First video showcase of ExtraBiomes.
Ancetras - Love that texture pack.
Delocuro - textures for biome colored leaves.
SirSengir - For providing a great example of a simple yet powerful API
Eloraam - For graciously providing help with RedPower integration
AtomicStryker - For helping with the final step of porting to bukkit
mushroomhostage - For embracing the job of porting to bukkit
Rorax - For providing great data regarding Forestry bee generation and testing the fix.
mistaqur - For embracing the concept of opensource and being the first community member to fix a bug and add a feature.
MrAndrew420 - For being the first to embrace the wiki and post screenshots of nearly every biome
ExterminatorJeff - Former developer
bspkrs - For fixing up a build script for Ant :D

The Buildcraft Development Team
  Extrabiomes XL uses a modified version of OilPopulate.java from BuildCraft.
  The modified source is available here:
  https://github.com/ScottKillen/ExtrabiomesXL/tree/master/extrabiomes/src/common/extrabiomes/plugins/buildcraft
  BuildCraft is distributed under the Minecraft Mod Public License 1.0 at
  https://github.com/SirSengir/BuildCraft/
