GAHA, or Gaelen's Antiquated Homestead Adventures, is a modpack created and used by the Virtual Twitch Streamer GaelenTV for their TerraFirmaCraft stream series. Released for the purpose of letting their viewers enjoy the TerraFirmaCraft experience for themselves, it emphasizes the progress of the TerraFirmaCraft mod while dealing with the less enjoyable parts of the grind, such as generally slow character movement between different points on the map, and adding some other things to do after the player has achieved red steel and has access to the Nether.
TerraFirmaCraft is a mod where wooden tools don't exist. You knap your first tools from two rocks you found on the ground, find copper, make metal tools, and go from there. Exploration is key: Certain stone layers contain certain metals, and you'll need to search far and wide for the right rocks that contain the right ores. Time matters, too: Different seasons increase or decrease the temperature, and crops need plenty of time to grow into the food you will subsist off of in order to survive in the world, but only have certain levels of acceptable temperature and rainfall. Planting at the right times will give you plenty of food through the more aggressive times of the year and will allow you to find those valuable ores without fear of starvation.
Since the Nether otherwise doesn't have much to do inside it once you've gotten there in TerraFirmaCraft, Tinkers' Construct and other such mods have been added to allow the player to work their way up to TCon's endgame ores: Cobalt, Ardite and Manyullyn. Additionally, numerous ores were added via TFC:Metallum to increase the number of metal options for the player and allow them more mines to dot the world, with which they can pull tasty, tasty ores and forge tastier and potentially more lucrative tools, weapons, and other such doodads.
To help spice up the player's diet, Pam's HarvestCraft has been implemented as to increase the number of staple foods they can hoard in their larders, as well as increase the number of different cooked foods they can enjoy while trying so hard to maximize their health. Additionally, thanks to TFC Homestead, the food they can store will last for much longer, their livestock will give more produce the happier they are, and with it and Macaw's Furniture, they can even spruce up their homestead further with actual furniture!
There's even some quality of life shoveled in to help give streamers less eerie silence and less eye strain. Because TFC Homestead adds aged drinks that have a chance to apply the Nausea status, Custom Nausea reduces the effect of the status by 75%, which definitely helps with the whole "kinda need to see" part of streaming, and Infinite Music sets the time of silence between each track that plays to 0, so you don't have to worry too much about filling the silence between tracks with something that might get hit by a DMCA claim.