Gunstruction is now available for iOS devices! I have been playing with the beta release for some time now and it is a lot of fun and very useful.
The iOS app is a lot like the website but the touch interface makes it even easier to move around and build exactly what you want. It may seem like it is just a fun app (and it is fun) but it is actually a powerful tool for planning an AR-15 build. I recently wrote an article about how truly lightweight AR-15 builds take planning and the great thing about Gunstruction is that the weight of each component is included. It is probably the most complete repository or weight data available.