pool.ntp.org
List of stratum-1 servers
List of stratum-2 servers
List of servers with NTS support
ChronyControl — install and configure chronyd on macOS
Ansible chrony roles
Augeas chrony module
collectd chrony plugin
Munin chrony plugin
Nagios chrony check
Prometheus Node exporter
Prometheus Chrony exporter
Telegraf chrony plugin
Zabbix chrony template
chrony-graph — generate graphs from chrony logs
chrony_ntp_logconv — convert chrony logs for ntpviz
ntp2chrony — convert ntp configuration to chrony
timedatex — systemd-timedated replacement
Command and monitoring protocol in Java
GPSd — a GPS service daemon
ntp-refclock — Wrapper for ntpd drivers
Radio Clock
OmniSync
rpi_gpio_ntp
leapshm
pps-gpio-poll
Security audit(archived from original)
Handling leap seconds
Ethernet timestamp calibration
Linux PPS utilities
NTP/PTP performance testing
Clock and network simulator
Fuzz testing of chrony
GPSD Time Service HOWTO
Documents of IETF NTP working group
NTP
NTPsec
OpenNTPD
BusyBox
ConnMan
dntpd
ntpclient
systemd-timesyncd
rsntp