Pushover is a messaging system that is easy for programmers and manufacturers to implement but not so easy to setup and manage, mostly due to the lack of documentation.
Pushover does not require an executeable to send messages, set a few variables and an HTTP post will successfully send a message. I use the powershell example below to send test messages.
$parameters = New-Object System.Collections.Specialized.NameValueCollection
$parameters.Add(“message”, “Test from server 10.118.1.54 to My Phone”)
$client = New-Object System.Net.WebClient
The token value above is the Application that the message comes From. Users can subscribe to this Application to receive alerts. When a user subscribes they get a virtual token that does not match their assigned user token. I believe this exists to keep their user token private.
The user value is associated with a user OR a group. If you pay for Pushover Teams you can manually add user tokens to a group and a memo field lets you keep track of what token belongs to whom.
Any user can create an application in the Pushover web interface, its just a random number that messages can come from and users can subscribe to.
Some info can be gleaned from reading their API docs here. https://pushover.net/api/client#register