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Kill Bill

A decade of production billing under Apache 2.0, with no gated features and everything pluggable.

What it is

A Java-based, plugin-driven billing platform maintained for over ten years. Every component — tax engine, invoice formatter, payment gateway, usage calculator — can be swapped via plugins. Data lives in a relational database (MySQL or PostgreSQL) that the operator controls. Its catalog system handles add-ons, billing alignment and proration for genuinely complex enterprise scenarios.

Key facts
Category Billing layer (fully open source)
Licence Apache 2.0 — no paid tiers, no feature gating
Language Java (plugin/OSGi architecture)
Deployment Self-hosted or cloud
Usage metering Plugin-based
Data access Direct database + plugins + API
Multi-tenancy Built in
Business model Consulting and support services

Strengths

  • Ten years of production use in complex enterprise environments
  • Completely free with nothing gated
  • Most flexible architecture in the category — everything is pluggable
  • No vendor lock-in whatsoever

Limitations

  • Steep learning curve; Java/OSGi knowledge required
  • Heavy setup and operational cost
  • Documentation is functional but dated
  • Smaller community than Lago's
  • Dated UI/UX

Relevance to Tidemill

Kill Bill is the third integration priority — a smaller but loyal user base whose billing logic is already heavily customised. That customisation is exactly why these users need auditable, configurable metric computation: generic formulas are least likely to match their reality. See Metric Transparency.

Like Lago, it is a same-database connector — DatabaseConnector rather than WebhookConnector — querying the billing engine's tables directly with no ETL. See connectors.

Status: P1, not yet implemented. tidemill/connectors/killbill.py is planned.

Sources