Matrix is:
an open standard for decentralised communication, providing simple HTTP APIs and open source reference implementations for securely distributing and persisting JSON over an open federation of servers.
It's pretty fantastic, if you think on the massive problem of fragmentation all across the web. They've created an easy to use API, and you can do a kludgy test using curl from the terminal (*nix, mac, win). See: http://matrix.org/docs/howtos/client-server.html
It's pretty straightforward to do a quick test. I have an account at https://matrix.org / https://vector.im, so I used that to get a token.
curl -XPOST -d '{"type":"m.login.password", "user":"myuserid", "password":"mypass"}' "https://matrix.org/_matrix/client/r0/login"
That returns the token in some json:
{"access_token":"MDAxO...blahblah","refresh_token":"MDAxO...blahblah","home_server":"matrix.org","user_id":"@myuserid:matrix.org"}
Now you have the access_token you can use in your curl command, when hitting the API, and I understand that this token does not expire. Also get the ID from a room you create at matrix.org (get room properties via the web UI), which for me was !QaRABAkxDBNukDoCOY. The ! is problematic in shells so, escape it after you paste the room id into your curl command.
Think of the curl command as a really, really simple analogue to a proper matrix.org client like vector.im, so, the URL of the API is that of your home server; in this case matrix.org. (Thanks @Half-Shot)
curl -XPOST -d '{"msgtype":"m.text", "body":"Hello from '"$USER"'"}' "https://matrix.org/_matrix/client/r0/rooms/\!QaRABAkxDBNukDoCOY:matrix.org/send/m.room.message?access_token=MDAxO...blahblah"
You can use shell variables in your curl command, but you have to split the data part using single quotes. The json's structure makes this a little confusing, but it's basically:
... -d 'whatever'"$thevar"'whatever' "https..."
Now it should be working, and you could now shell script it, separating those long strings out into variables, and pulling in, say, a $1 arg to make it easy to ping a certain room with messages from your servers. I.e. something like:
> matrixlog "did a yum update"