There are a lot of components, but the three main ones are:
- Yarn stash & yarn detail
- Needle and hook inventory
- Project list & project detail
The Knit Buddy app also includes a place to catalog knitting books, a "stitchionary" with cable, colorwork, and other patterns, a "how-to" section for knitting and crocheting, terms and abbreviations, and a tool for substituting yarn. The app was really well thought out, and unlike some, I'm guessing that they had actual knitters use it for awhile and give feedback. I.e., it is actually useful for a real knitter, not what a non-knitting programmer might guess that a knitter would need and use.
I understand from comments in the App Store that at one time this app synced over multiple devices so you could have it on both your iPhone and iPad, but only have to enter information in one place, but that functionality was removed in a recent update. I need it on my phone the most since that is what I always have with me, but it would be nice to be able to enter information on the iPad and have it sync between them. I wonder if that's something they may add back into the app, given all of the negative comments, but I don't know the reason they removed it in the first place.