I have worked with PRTG for more then 6 years. This company is very reputable and is great for monitoring uptime and service level agreements for services. It also allows you to configure a Mail Server to receive alerts via email/text message/etc. It’s also FREE, you can’t beat free!
You can specify domain accounts using LDAP for automatic account provisioning.
In the upper right you can review what services are online, down sensors, paused alerts etc.
You can also specify whatever sensor you wish using SNMP.
If you want to get really granular you can use SNMP to notify you of hardware failures!