LiteLLM solves a similar problem to OpenRouter, calling many different LLM providers through one consistent interface, but as a library and self-hostable proxy server rather than a hosted marketplace. A developer can call Anthropic, Google, Azure OpenAI, or a self-hosted model through the exact same OpenAI-style function signature, which makes switching providers, or supporting several at once, a configuration change rather than a rewrite.
Its proxy server mode adds features more relevant to running it as shared infrastructure for a team: load balancing across multiple API keys or providers, cost tracking per user or project, and rate limiting, letting an organization centralize how its various applications access different LLMs rather than each one managing its own provider credentials and logic separately.
Being free, open source, and self-hostable, it appeals specifically to teams that want OpenRouter-style provider abstraction but running on their own infrastructure rather than through a third party sitting between their application and the model providers, trading OpenRouter's convenience for direct control over routing logic and data flow.