The way I would describe Prometheus in relation to those other tools:

- Prometheus is open-source and self-hosted.

- Prometheus is about dimensional numeric time series metrics only (no log-based analysis, no per-request tracing, etc.).

- Prometheus has a strong focus on systems and service monitoring, not so much on business metrics.

- Prometheus is more of a Swiss army knife of monitoring rather than a ready-to-drop-in package that starts monitoring everything automatically.

- Prometheus is very much about whitebox monitoring and manually defining any metrics that could be useful for you (although we support blackbox exporting and bridging metrics from existing systems as well).

- We don't do machine-learning-style anomaly detection, but we do alerting based on manually defined rules.

- For a purely metrics-based solution, the insight we deliver is one of the best in the field (via the dimensional data model and the query language to go with it).

- Many open-source projects are starting to expose native Prometheus metrics (like k8s, etcd, ...), which gives Prometheus an advantage when being used together with those.

EDIT: Also try the "Getting Started" tutorial - that should only take a couple of minutes to try it out: https://prometheus.io/docs/introduction/getting_started/