I have created a new mod for 1.12.2 and 1.16.5, mainly for personal use, but also posted to CurseForge. Time Shall Not Pass! is a server-side mod that essentially keeps the daylight cycle from progressing when no players are online. Something of which is possible to do with command blocks, I know, however with this mod the state of the gamerule only changes when players connect/disconnect. Thus is quite a bit more efficient than the command block counter-part, as well as not cluttering the server console/chat log and causing you to have to turn off command output.
I have recently started a personal server for some friends using a new modpack which includes Lycanites mobs and Serene Seasons, both of which are affected by the daylight cycle. So I wanted to make sure the daylight cycle is not on when no one is online, and wasn't happy about having command blocks under spawn to do this job. My mod also allows for certain players to be excluded based on UUID in the config, meaning that they will not cause the daylight cycle to toggle when logging in or out of a server. Thought it might be nice to allow certain accounts, like spectator accounts and such, to be capable of logging on without affecting things.
It may not be useful for most people, but I'm hoping there is some people out there that might find use for it. I used to run a vanilla SMP, this was before I really knew much about command blocks, and would always be upset that the day counter was in the thousands even though the server had plenty of time where no one was online (jobs, school, etc.). Maybe it's just me.