It is relatively simple, but seems like it could be useful. While everything included is something you could just print out and keep with your spinning equipment, I know that I am forever misplacing stacks of paper and books and so realize that this could come in handy.
The program is divided into sections including: Twist Angle, WPI Guage, TPI Gauge and a series of calculators. I have not actively used this during spinning yet (as I have been working on my 12th Night projects), but plan to do so when I get back to my Icelandic yarn spinning next week. I have been trying to get a consistent grist in my yarn, but have not been paying as much attention to things like the the angle of twist. On some level, I knew that was important, but was having a hard enough time managing the wool drafting process that I figured I would learn things one step at a time. Given that I plan to weave what I am spinning, I think now is the time. I don't want a project to go all wonky after it comes off the loom and is wet-finished.
More info about the app is here: http://www.ashlandsky.com/as/apps.html
I purchased this one last week and am already thrilled with it. I do not have the funds to purchase a full weaving software package (and do not feel I need it given that I am not using a computerized loom) and this app gave me an inexpensive way to play around with threading and treadling combinations to see what they produce (and to get a better understanding of the actual weaving mechanics).
Even before I got a loom I had Deborah Chandler's Learning to Weave. I did the practice exercises in the book and this helped me understand how to read and create weaving drafts. I am glad I did that, because I could already read a draft when I did my first project. What this program does, however, is simplify the draw down on the draft.
I spent time time yesterday adding patterns from the Birka textiles and then just played around creating my own combinations to see what would happen.
The image attached is a screenshot from my phone, but you can also export the drafts as WIF files so that you can share them with others or use them in another weaving program.
Also available is a warp/weft calculator and, the item I am most excited about, a threading and treadling tracker! You tap the screen each time you thread a heddle or treadle and it progresses to the next in the sequence. I will have to figure out a way to keep my phone in a very handy spot while weaving, but I definitely intend to try out the treadle tracker on my next project (which will be the Birka broken diamond twill in my screenshot). If I love it I might add the program to my older iPhone (now used as an iPod) and keep that one in the weaving room and use it specifically for this.
More information about the app can be found here: http://www.weaveit.com/iWeaveIt.aspx