How can I send a notification to a Windows 10 computer from the command line

Another way is the built in MSG.exe command that has been there since Vista. From a command prompt there the following:

msg /server:poseidon daniel "Please contact help desk immediately!"

Server is the name of computer you are sending the message to and daniel is a valid user name of the person using that computer. Fast and simple without any extra downloads.

If you want to create a native windows notification (a popup in bottom-right corner and persistant in notification center), you could take the following Powershell snippet as a template.

Taken from https://stackoverflow.com/a/47123275/1043209

[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms")

$objNotifyIcon = New-Object System.Windows.Forms.NotifyIcon

$objNotifyIcon.Icon = [System.Drawing.SystemIcons]::Information
$objNotifyIcon.BalloonTipIcon = "Info" 
$objNotifyIcon.BalloonTipText = "wzzup this is a title." 
$objNotifyIcon.BalloonTipTitle = "WHATS UPPP THIS IS A PARAGRAPH!"
$objNotifyIcon.Visible = $True

$objNotifyIcon.ShowBalloonTip(10000)
Start-Sleep 500

It looks like this in notification center.

You can use Growl for Windows for this. You'd need growlnotify to send the message and the full application where you receive the notification. As per the comments you will need a plugin for native toast notifications.

On the receiving end, you will also need to enable notifications from other PCs and to set up a password.

We're assuming the system where the full GFW package is installed is 192.168.1.110.

On the sending end growlnotify.com /r:"test1" /a:"test1" /host:192.168.1.110 /pass:test boo registers the application. You need to do this once I prefer the batch varient here cause it has more useful warnings for initial setup. You can switch to the exe file once you know things work.

and something like growlnotify.com /n:"test1" /a:"test1" /host:192.168.1.110 /pass:test /t:title message would work after that to send messages.

For anything else, you can probably refer to the docs and hack together something to fill in the message content.

Tested between two windows 10 systems and it works for me.

If you want to send messages from linux to a GFW or growl for mac instance, you can use gntp-send