We built a (free) tool that tracks deprecation warnings at runtime (ruby only for now). It's a gem you install that works like Sentry or Rollbar, but aggregates deprecation warnings instead of exceptions. Docs are at https://docs.infield.ai/docs/monitor-deprecation-warnings

We built this because we rely on deprecation warnings at Infield as one piece of safely upgrading large Rails apps. Often large apps don't have perfect test coverage of all their gem usage, or use different codepaths in staging/prod than you on CI. There are good existing open source tools like https://github.com/Shopify/deprecation_toolkit for tracking deprecations in your CI suite but they don't work well in prod.

Our tool works as an open source gem that you install (https://github.com/infieldai/infield-ruby) which spins up a background thread that collects deprecation warnings and reports them to our API. We aggregate them there and track them over time so you can verify you've addressed them before you push an upgrade. It works for any deprecation that goes through ActiveSupport::Deprecation, which covers Rails and a bunch of Ruby gems but not ruby itself (that'll come!).