Best open-source alternatives to OpenAI Agents API

Omnara is an open-source platform for managing and running AI agents. It is aimed at developers and teams that want to launch agents through an API, the CLI, a dashboard, or an SDK, while keeping control over models, tools, permissions, and execution environments. The project positions itself as a self-hostable alternative to hosted agent platforms. The system is built around a REST API, a worker-based execution model, and persistent storage for agent state. It can run agents against multiple model providers, use built-in or custom tools, and execute tasks on connected machines or sandboxes. The README also describes integrations for Slack, Discord, GitHub, and scheduled triggers, making it suitable for automated workflows and collaborative agent operations.

Letta is a project for building stateful AI agents that retain memory and improve over time. It is aimed at developers who want to run agents locally or self-host them, and it also connects to browser-based and messaging-channel experiences. The README points users to the current codebase, which includes an agent harness, terminal UI, App Server, channels, and the runtime used by the desktop and web apps. It can be installed from npm, launched as a local CLI, or run as a server for self-hosted agents. The project also integrates with Letta Cloud to keep agent memory, identity, and conversations available across computers, and it provides documentation plus an agent SDK for TypeScript applications.