Syncthing

There is very many sync tools around, but most have this thing about using a server
to sync the things between different devices, which means that either you need to
have a machine that can act as the server, or you need to trust somebody else
with your data.
If you have a computer not being utilized very much this would probably be fine,
but then again you could probably find a better use for this machine than serving as
a file server essentially.
The technological solution to this problem is to use syncthing, the serverless sync tool
just set it up on the machines you need to sync set the desired folders and do the sync.

There is a reasonable amount of things you can configure syncthing to do, I use this to
sync several files between my phone and my computer, keeping stuff up to date without
having to use cloud apps.

Things syncthing does not do.

Syncthing will not sync your tools over the internet it is a requirement
that they are on the same network, so if you aren't getting to your computer regularly
it might be the right solution for you.
But as far as I can see that is the only downside, if you consider it a downside.

Features

Syncthing will give you a lot of parameters to configure it in the webui, the fact
that it is a webui is not a big deal there is still plenty of nobs to turn and it works very well
there might be other uis but I tend to not really use them very much.

If you have a file that will change very much and you want it to update the file rather than
do nothing, you need to set some sort of version control in syncthing, at least that is what I had to
do with my calendar, but that was easy to do so no problem about that.

In fact I find syncthing to be a excellent tool for sync'ing different devices for commonly used files.