Most of my work is on libarchive and the associated tools, including tar, cpio, and pax. I've been quite gratified by the reception libarchive has received and the variety of different ways it's being used. Ongoing development of the portable libarchive suite is occurring at github.com/libarchive
I've recently started working with FreeBSD/ARM on the Raspberry Pi, BeagleBone, and other boards. That includes a system build tool called Crochet.