Lago is an open-source billing and metering platform that lets companies build usage-based, subscription, and hybrid pricing models without building a homegrown billing stack from scratch. Founded in 2021 by two early Qonto employees, it offers a free, self-hostable core plus managed cloud tiers, and is used by companies such as Mistral AI, PayPal, Groq and Synthesia to meter events and issue invoices at scale.
PostHog is an all-in-one, open-source developer platform that bundles product analytics, web analytics, session replay, feature flags, A/B testing, experiments, surveys, error tracking, a customer data platform, and a data warehouse into a single stack engineers can self-host or run in the cloud. Founded in 2020 by James Hawkins and Tim Glaser through Y Combinator, it lets product engineers track usage, ship features, and keep customer data in one place rather than stitching together a dozen SaaS tools. The company reached unicorn status in 2025 with a $75M Series E at a $1.4B valuation.