I am breaking from tradition this week by featuring Apple's Open Source libc implementation. Unlike previous featured libraries, which are directly usable in an embedded system, I mostly use Apple's libc implementation as a reference.
The later revisions of libc have a lot of assembly code which is not directly usable on my systems. I also find that newer implementations are not necessarily to my liking, often featuring types or requiring functionality that I don't want to implement.
However, one of the great benefits of the libc source is that there are a great many implemenations. Some of the older libc versions (such as libc-186) use primarily C files. If you travel back in time or use a Google search, you can often find a version that you like or can use as a starting point.
I highly recommend using this library as a reference and importing what you need. I have used this code in multiple projects, and you will see many functions featured in