New Relic One is a monitoring and observability tool that helps developers identify performance issues in their production applications. The tool can be integrated with CodeStream, an IDE extension, to provide direct access to the source of errors in the code. This integration allows developers to quickly diagnose and fix issues without leaving their IDE. With New Relic One, developers can track telemetry data, detect anomalies, and set up error monitoring for their Elixir applications, including those built with Phoenix. The tool provides a free account option that includes 100 GB/month of free data ingest, one free full-access user, and unlimited free basic users.