Prometheus is a widely adopted open-source monitoring and alerting toolkit originally built by SoundCloud in 2012. It provides four key features: a time-series database, a robust query language called PromQL, a pull-mode "scraper" for retrieving and storing metrics, and an alerter component for customized notifications. Prometheus has become the de facto standard for monitoring Kubernetes applications, with many organizations using it to collect metrics from their infrastructure and services. However, as the size of observability environments grows, Prometheus faces challenges such as single-server architecture, memory utilization, long-term data storage, and lack of "hybrid observability". Several alternatives are emerging, including Grafana Mimir, VictoriaMetrics, Promscale, and Thanos, which aim to address these challenges with improved scalability, performance, and feature sets. As the landscape continues to evolve, it's essential for users to stay informed about new developments and potential successors to Prometheus in the observability space.