iOS 7 Line Icons
This is actually a paid iconset, but there is a free version.
iOS 7 Line Icons is a free Icon design resource made by Dribbble user Chirag Dave. As far as I can tell, its license is Creative Commons Attribution.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.
