This package is built from the binaries provided in the officially endorsed community-built package for Marvell 88F6281-based Synology NASes. Unfortunately, 1.4.0 is the most recent version of the binary package which is available from the vendor's repository.
Install script adds user "zerotier-one" and group "zerotier-one" as the daemon drops privileges if such user and group exist. I chose UID & GID to be 64000 for these.
This is my first attempt at creating an ArchLinux package, please let me know if anything should be improved.
EDIT: One could wonder what's the use of outdated software on outdated hardware. Well, I just dusted off a long-forgotten PogoPlug Series 4 and installed a new instance of ALARM on it. Then I thought about making it a jumpbox for my virtual ZeroTier LAN. Initial testing showed that it's able to handle ~30 Mbps traffic via ZeroTier, which is more than enough for my purposes. This little box is definitely going to stay powered on. Perhaps I'll find enough energy to cross-compile the current release of ZeroTier for ARMv5. So far I'm good with 1.4.0.