HTTP Time Protocol is a time synchronization tool that uses Web server responses (HTTP headers) instead of the NTP protocol. If you are behind a corporate firewall, NAT device, or proxy server, HTP will still be able to synchronize the time. For high precision time synchronization, use ntpd.
NTPmon is a Web-based monitor for (usually LAN-based) NTP servers. It provides a small number of health metrics that help to locate NTP configuration or operational trouble spots. It uses RRDtool as its storage and graphing engine, and provides a CGI script for viewing the results.
rpi_gpio_ntp enables you to connect a GPS module with a PPS signal (or any other PPS source) to a Raspberry Pi, then sync the local clock using NTP. This can give you very accurate timekeeping. When you use this program, you do not need to patch the kernel to get PPS support, and do not need to patch the NTP program.
s6-networking is a collection of small Unix tools designed to help networking. It includes clock synchronization, Unix and TCP super-servers, Unix and TCP access control, and other miscellaneous utilities. It is particularly suited for management of clients and servers on embedded devices, but works just as well on larger systems.