The Zeta SMP modpack adds several new structures, creatures, biomes etc to promote exploration, but is designed to be lightweight to make it easily playable on lower-end devices. This allows players (who may have limited RAM and CPU) to play with enough mods to change the game's meta, but not enough to cause significant lag. Mods like Biomes O' Plenty and Mo' Creatures add more content to the game, promoting exploration. There are also several mods added to make multiplayer servers a lot more fun, such as the Hats mod and Inventory Pets!
Modlist:
Additional Structures
AutoRegLib
Baubles
BetterFPS
Biomes O' Plenty
Blood Magic
Chameleon
CoroUtil
Cucumber Library
Custom Mob Spawner
Defiled Lands
Dynamic Surroundings
Guide-API
Hats
iChunUtil
Inventory Pets
JourneyMap
Just Enough Items
Macaw's Bridges
Macaw's Doors
Macaw's Fences
Macaw's Furniture
Macaw's Roofs
Macaw's Windows
Mo' Creatures
Mo' Villages
MrCrayfish's Furniture
Mystical Agriculture
Neat
OreLib
Ores Above Diamonds
Pam's Harvestcraft
Quark
Roguelike Dungeons
Ruins
Spartan Shields
Storage Drawers
The Legend of Herobrine
Traveler's Backpack
Waystones
Weather, Storms & Tornadoes