I wanted to start this discussion to see what other MSP's are using regarding free open source software. I'll start...
most of yours + veeam/idrive for backups and replications, check central, uptimerobot, virtualmin
I know it's a bit unorthadox, but many of our clients use a mixture of UNRAID and Ubuntu server for docker and file storage.
Unfortunately these are usually the same clients that just refuse to spend money where it's often needed.
Using UptimeKuma instead of Uptime robot for some monitoring
LibreNMS - Integrated into slack / teams for alerting and monitoring