Backstage

Backstage is an open-source framework for building developer portals, designed to unify infrastructure tooling, services, and documentation. It features a centralized software catalog, software templates for quick project setup, and TechDocs for documentation. Its extensibility through a rich plugin ecosystem allows organizations to customize and integrate various tools and services into a single, streamlined development environment.

Backstage is an open-source framework for building developer portals, which aligns with the concept of a low-code platform for internal tools. While it doesn't explicitly market itself as 'low-code' or 'drag-and-drop UI builder' in the same way Retool does, its plugin-based architecture and software templates enable rapid development and customization of internal applications. It offers extensive API and database integrations through its catalog and plugins, allows for code customization (being an open-source framework), provides access control and security features, and supports flexible deployments. Many 'other' features like debugging tools, version control integration, audit logs, workflow automation, prebuilt components (plugins), AI assistance (via plugins), and custom theming are also present or achievable through its extensible plugin ecosystem.