1. Data Source Compatibility: Grafana focuses on visualization and dashboarding, supporting a wide range of data sources including Prometheus, InfluxDB, Elasticsearch, and more. On the other hand, Prometheus is primarily a monitoring tool designed for metrics collection, storage, and alerting. Sensu, similar to Prometheus, is also focused on monitoring, but it supports various cloud-native data sources and plugins, making it highly extensible.

2. Data Collection Method: Grafana does not collect data itself but relies on other tools like Prometheus or InfluxDB for gathering metrics. Prometheus, on the contrary, uses its own time-series database and pull-based model for collecting metrics from monitored targets. Sensu follows a similar approach as Prometheus, utilizing agents on monitored hosts to collect data and send it to the central server for processing.

3. Alerting Capabilities: Grafana offers basic alerting features like threshold-based alerts which are suitable for simple use cases. In comparison, Prometheus has a robust alerting system that allows users to define complex alerting rules using PromQL queries. Sensu also provides comprehensive alerting capabilities, supporting various alert handlers and integrations with messaging platforms.

4. Extensibility and Customization: Grafana provides a high level of customization through its plugins and integrations with various data sources and visualization options. Prometheus, although less focused on visualization, offers flexibility through exporters and integrations with other monitoring tools. Sensu excels in extensibility, enabling users to create custom plugins, handlers, and checks to tailor the monitoring setup to their specific needs.

5. Community Support and Ecosystem: Grafana benefits from a large and active community, resulting in a vast library of plugins, dashboards, and resources for users. Prometheus also has a strong community backing, with a well-established ecosystem of exporters, integrations, and third-party tools. Sensu, although not as widely adopted as Grafana and Prometheus, has a dedicated community that contributes to its plugins and extensions.

6. Architecture and Scalability: Grafana follows a client-server architecture where the server interacts with data sources and serves dashboard requests. Prometheus is designed with a server that scrapes metrics from targets and stores them locally. Sensu employs a distributed architecture where agents collect data and send it to a central server for processing and alerting, making it suitable for large-scale deployments.

In Summary, the key differences between Grafana, Prometheus, and Sensu lie in their focus on visualization vs monitoring, data collection methods, alerting capabilities, extensibility, community support, and architectural design.