The Willpack

The Willpack is a technology focused mod, adding electricity generation and machines from IC2, Buildcraft, Applied Energistics 2, Modular Powersuits (allows crafting of modular power armor), ICBM (missile fun!), RailCraft, ProjectRed (enhances redstone capabilities - adds redstone wire, additional logic etc.) and Atomic Science.

Also includes:

Galacticraft for space exploration
Harvestry and Pam's HarvestCraft for farming/food mods
Thaumcraft for some magic/research gameplay.

In addition to the these major gameplay mods, the pack also includes some of the following quality of life modes:

Treecapitator - Cut down entire trees by breaking a single block (take longer to cut but returns the whole trees materials)
Dynamic Trees - Overhauls the appearance of trees making them look pretty
Dynamic Surroundings - Makes the world look nicer, adds ambient sounds
Better Foliage - Improves grass ground coverings and tree leaves etc.
Biomes O' Plenty - Adds additional biomes and improves existing biomes
Just Enough Items - UI crafting book for all items in the game
Basic Nether Ores - Addes ore to the nether
JourneyMap - Adds minimap and overworld map that reveals as you explore and shows enemies
ConnectedTexuresMod - For pretty connected textures like glass panes

The full list of mods can be found below:

Advanced Machines

AE2 Stuff

Applied Energistics 2

Atomic Science

Basic Nether Ores [Forge/Fabric]

Better Advancements

Better Foliage

Biomes O' Plenty

Blockcraftery

Buildcraft

Chicken Chunks 1.8.+

CodeChicken Lib 1.8.+

Compact Solars

ConnectedTexturesMod

Dynamc Surroundings

Dynamic Lights

Dynamic Trees

Dynamic Trees - Biomes O' Plenty Compat

Dynamic Trees - Industrial Craft 2

Dynamic Trees - Pam's HarvestCraft Compat

Dynamic Trees - Thaumcraft Compat

Energy Converters

Forestry

Galacticraft

Hammer Microblocks

ICBM

Industrial Craft

Inventory Tweaks

JourneyMap

Just Enough Energistics

Just Enough HarvestCraft

Just Enough Items

Logistics Pipes

Modular Powersuits

No Recipe Book

Pam's HarvestCraft

Project Red

Railcraft

Thaumcraft

Thaumic Energistics

Treecapitator Updated

UniDict

Unloader

VanillaFix

Waila harvestability