Sequel

Database toolkit for Ruby combining a low-level SQL builder with a full ORM layer. Provides thread safety, connection pooling, and a concise DSL for constructing queries and table schemas while mapping records to Ruby objects and handling associations.

Mature Ruby database library maintained since the mid-2000s. Differentiates from ActiveRecord by focusing on datasets and chainable queries instead of Active Record patterns, offering a lighter-weight alternative for applications outside Rails or teams preferring explicit query construction over convention-heavy abstractions.

Key capabilities:

• Dataset-based query API with chainability and lazy evaluation
• Broad adapter support: PostgreSQL, MySQL, SQLite, Oracle, SQL Server via TinyTDS, IBM DB, JDBC, ODBC, and more
• Prepared statements, bound variables, savepoints, two-phase commit, and transaction isolation
• Primary and replica configurations with database sharding support
• Built-in migrations, schema dumping, and bin/sequel console for ad-hoc database access

Backend APIs, data pipelines, and reporting tools benefit from Sequel's explicit control over SQL generation. Developers working with non-Rails stacks or needing fine-grained query optimization use it as a drop-in alternative. Integrates with Rack-based frameworks and standalone Ruby scripts for quick database introspection and scripting.