Best Open Source LLM Application Frameworks using Vitest in 2026

CopilotKit

Build AI copilots for your product in hours, not months

Stars
31,400
Forks
4,058
Last commit
11 hours ago

Integrate production-ready AI copilots into any product quickly and easily with CopilotKit's open-source platform.

Open Source Alternative to:

LangChain

FastGPT

Build powerful AI knowledge bases with ease

Stars
28,029
Forks
7,092
Last commit
18 hours ago

FastGPT is a free, open-source platform for creating AI-powered knowledge bases with data processing, model invocation, and visual workflows.

Open Source Alternative to:

Zendesk

Langfuse

Open source LLM engineering platform for AI-powered applications

Stars
27,209
Forks
2,768
Last commit
12 hours ago

Langfuse provides tracing, evaluations, prompt management, and analytics to debug and improve LLM applications.

Open Source Alternative to:

LangSmith

Arize Phoenix

Open-source LLM tracing & evaluation for AI optimization

Stars
9,673
Forks
870
Last commit
11 hours ago

Open-source platform for LLM tracing, evaluation, and optimization. Features automatic instrumentation, prompt playground, and real-time AI application monitoring.

Open Source Alternative to:

LangSmith

Trieve

AI-powered search and RAG platform for faster, more relevant results

Stars
2,653
Forks
242
Last commit
4 months ago

Trieve offers an all-in-one solution for search, recommendations, and RAG with automatic continuous improvement based on user feedback.

Open Source Alternative to:

Pinecone

Stars
Forks
Last commit

Stars
Forks
Last commit

Stars
Forks
Last commit

Stars
Forks
Last commit

Stars
Forks
Last commit

Stars
Forks
Last commit

CopilotKit

Build AI copilots for your product in hours, not months

Stars
31,400
Forks
4,058
Last commit
11 hours ago

Integrate production-ready AI copilots into any product quickly and easily with CopilotKit's open-source platform.

Open Source Alternative to:

LangChain

FastGPT

Build powerful AI knowledge bases with ease

Stars
28,029
Forks
7,092
Last commit
18 hours ago

FastGPT is a free, open-source platform for creating AI-powered knowledge bases with data processing, model invocation, and visual workflows.

Open Source Alternative to:

Zendesk

Langfuse

Open source LLM engineering platform for AI-powered applications

Stars
27,209
Forks
2,768
Last commit
12 hours ago

Langfuse provides tracing, evaluations, prompt management, and analytics to debug and improve LLM applications.

Open Source Alternative to:

LangSmith

Arize Phoenix

Open-source LLM tracing & evaluation for AI optimization

Stars
9,673
Forks
870
Last commit
11 hours ago

Open-source platform for LLM tracing, evaluation, and optimization. Features automatic instrumentation, prompt playground, and real-time AI application monitoring.

Open Source Alternative to:

LangSmith

Trieve

AI-powered search and RAG platform for faster, more relevant results

Stars
2,653
Forks
242
Last commit
4 months ago

Trieve offers an all-in-one solution for search, recommendations, and RAG with automatic continuous improvement based on user feedback.

Open Source Alternative to:

Pinecone

Open Source LLM Application Frameworks using Vitest

A curated collection of the best open source frameworks specifically for building applications using Large Language Models. using Vitest.