Use pulseway . it's free and I use this and get push notifications for things like change of IP address, server down, restarts, os updates and cpu spikes. You can even remote see cpu usage charts, memory usage open command prompt and trigger reboots etc
I'm in the same boat as you. I've been testing Pulseway on few systems and it looks good. Nothing fancy as big players but powerful enough to get the work done. The best thing I like about it is the mobile app. You get all the alerts on the mobile app and user can initiate help request from the client and you can chat with them from your phone. They also have a "Dashboard", which I'm planning on displaying on a 50" screen in my office.
Try out Pulseway. We've been using it for the last two months and we couldn't be happier. It's without any doubt the best value for your money RMM. Who cares if the Microsoft Exchange System Attendant service crashed on your Exchange server if you can't remotely restart it easily? This app gives you the ability to implement corrective measures, which is huge...all from your mobile phone/tablet, etc.
Are you wanting to send them messages when the server is down or wanting to send them messages when something is grabbed and downloaded?
Not sure in SB, in sonarr you can set up multiple pushbullet accts to notify. It notifies when grabbed and downloaded.
For server down you could try one of these. I have seen them but not tried: https://uptimerobot.com/, http://www.pulseway.com
I've been using pulseway
It can monitor pretty well everything on the computer down to fan speed, you can get a command prompt from your phone. Remote control from the desktop. Alerting is very good But no ticketing and reporting is weak. It's around $2.00 - $2.50 per computer.
Do the demo, the mobile app is very powerful and the website and desktop programs are very good too.
The professional plan is $16 a system/year (Starting from 3). SaaS Enterprise starts from 50 systems, and that is $1,044 for the year. http://www.pulseway.com/pricing
And if you want to host your own Enterprise, its $720 for 50 systems for the whole year. http://www.pulseway.com/pricingonpremise
Pulseway can take care of all of the temps and voltages if you're system is capable of capturing them. It can also control and view all sorts of other stuff like who's logged in and the typical system resource usage stats.
Its not going to be something like dropbox. It will be something like http://www.pulseway.com or https://www.librato.com but much easier to work with. you will "connect" your Raspberry pi to the server and then the server will have a api that you can use to send commands to the Raspberry pi