Hosted on Heroku, using Sentry for error tracking, New Relic for performance monitoring, Sendgrid for email. Recently ditched Google Analytics in favor of Plausible for general analytics and Ahoy (Rails middleware) for deeper in-house analytics. Using Intercom for support/chat widget, but planning to switch to Chatwoot. Considering moving off Heroku, but the most obvious contender, Render, doesn't yet have high availability postgres with automatic failover.
Deployment is set up so any push to the master branch on GitHub is automatically deployed to production. Merging to the master branch can only be done via a PR, and needs green status from both linter (Rubocop), tests (Rspec run on CircleCI, both unit and integration) and coverage (100% test coverage required, verified by codecov.io).
UI is Bootstrap (but feeling long in the tooth), and server side rendering with a sprinkling of javascript. Still mulling over hotwire/turbo vs alpine vs stimulus vs react for some upcoming UI that requires more interactivity.