BusyBox is a software application that provides many standard Unix tools, much like the larger (but more capable) GNU Core Utilities. BusyBox is designed to be a small executable for use with the Linux kernel, which makes it ideal for use with embedded devices. It has been self-dubbed “The Swiss Army Knife of Embedded Linux”.
Pro version contains no ads or nag screens, uninstall feature, Advance Smart install feature, the ability to hand pick the applets you want, safety check for missing applets on start, and better overall support. The pro version will receive more frequent updates than the free version will.