If you're looking for a replacement for M/Monit, Datadog is a good candidate. Datadog offers an integrated monitoring and security platform that gives you real-time visibility into performance, security and user experience. It includes infrastructure monitoring, APM, synthetic monitoring, real user monitoring, security monitoring and serverless monitoring, so it's good for a wide range of industries.
Another good option is LogicMonitor, which offers a hybrid observability platform called LM Envision. It monitors everything in your on-premises and multi-cloud environments with real-time visibility and automation. The platform includes infrastructure, cloud and digital experience monitoring, as well as AIOPS for predicting and preventing IT problems. It's geared for MSPs, Enterprise IT and companies of all sizes.
If you want to go the AI route, check out Splunk. The company's platform combines modernized threat detection, investigation and response with full-stack observability. It's geared for large and complex organizations, with flexible and predictable pricing models that scale with the types of workload you run or the amount of data you ingest.
Last, Honeycomb is an observability platform that lets you zero in on the source of problems in distributed services. It includes distributed tracing, smart data sampling and debuggable SLOs. Honeycomb's unlimited custom attributes and event volume pricing means it's a good option for monitoring and troubleshooting that scales.