I am curious, is the NTP server based on an existing tool - specifically is it actually or based on ntpd or chronyd?

Thank you, Chris

Only Mikrotik devs know. Since ROS is closed source, I guess information you're interested in is a trade secret. I wouldn't hold my breathe while waiting to get an answer ...

NTP License

Copyright (c) David L. Mills 1992-2004

Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appears in all copies and that both the copyright notice and this permission notice appear in supporting documentation, and that the name University of Delaware not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. The University of Delaware makes no representations about the suitability this software for any purpose. It is provided "as is" without express or implied warranty.
http://www.ntp.org
https://support.ntp.org/bin/view/Main/SoftwareDownloads

NTP License

Copyright (c) David L. Mills 1992-2004...

As far as I could find, I saw that in the old EULA, but the current EULA (https://mikrotik.com/downloadterms.html) no longer mentions it. Is there a way to pull up the EULA from within RouterOS?

Only Mikrotik devs know. Since ROS is closed source, I guess information you're interested in is a trade secret. I wouldn't hold my breathe while waiting to get an answer ...

Usually, some amount of credit is required to integrate open-source code; so it should be relatively straight-forward to get an answer if they are using either tool.

EULA containing Mills' name doesn't mean that NTP implementation in ROS is actually a (trivial) recompile of Mills' NTP software ... it could only use a portion of it and include large amount of proprietary work. But it can also mean that the ROS NTP software is simply compiled Mills' software for appropriate platforms (and system libraries) - which I doubt.

I'm pretty sure that almost everything included in ROS is more ore less stripped down even if it's variant of "standard" utilities. For example, ntpd (NTP daemon) executable on x86-64 ubuntu 20.04 is 838kB and loads additional 670kB of system libraries (none include debug symbols which can take considerable amount of storage) ... while whole ROS (including kernel and what not) on arm (RBD52G) is around 15MB.

The ntp package on older ROS versions was definitely ntpd, but the NTP client/server on ROS 7 has a different behavior. I guess they wanted to get rid of ntpd, but wanted to keep the multicast, manycast and broadcast support, so they had to write their own thing.