From Digital Man to All on Sun Apr 4 15:44:25 2021
Synchronet v3.19 (the new version in development and in the "master" branch on gitlab.synchro.net), now requires the libarchive development package (e.g. libarchive-dev on Debian-based Linux distros) on Unix-like OSes. Or go to libarchive.org if you need to build from source for your OS/distro.
Windows sysops using the nightlies (not yet at v3.19, but should be tomorrow) should just automatically get libarchive.dll in the dev-update archive.