They have a version of the Ash shell, Berkeley licensed, with the original notice by Kenneth Almquist. The Busybox Ash is also derived from the same origin.
As others have pointed out, they also have their own libc.
Most of these decisions seem to have been made to avoid using the GPL outside of the kernel. And a custom libc seems to entail that patches have been necessary to enable some of the standard GNU based tools they do have. If I understand correctly, mainly because of Bionic, you often can't just take a standard piece of Linux userland software and make it work without modifications or without including the GNU libc.
Also because of avoiding the GPL, the hardware driver model is different, with most of the driver logic being in closed source userland code.
The filesystem layout is non-POSIX-like, the way the user accounts and processes are handled is non-standard, they have their own dynamic linker, etc. Not to mention that a large part of the system relies on their Dalvik (Java) virtual machine, with a large application framework implemented in C++ and Java through JNI.
I'm not familiar with the embedded Linux landscape, so I don't know if this heavy avoidance of the GPL is common there. But I do know Android does not resemble GNU/Linux for these reasons.