Okay, this might sound weird, but it really works to keep your hair soft. It's vinegar... regular old vinegar (white, red wine, apple cider) diluted 1:4 with warm water. You just pour a bit of it over your head then rinse it out after shampooing and it leaves your hair really really really soft. And it's not a "my hair is coated with synthetic smelling polymers" kind of soft -- it's soft like petting a (soft) goat or cat kind of soft.
This is my first batch -- I used apple cider vinegar and added a few drops of lemon essential oil. It smells like vinegar when you put it on, but after rinsing it out, there's no smell. I'm going to try white vinegar next.
I'm working on some home-made shampoo, too, but the first batch came out too thick -- it works great, but it's a paste, not a liquid, so I'm going to change some proportions on my next batch before I post the recipe here.