What Jan and Open WebUI each are
Jan and Open WebUI are both open-source ways to run AI models you control, and they are shaped differently. Jan is a desktop app that runs models on one machine. Its own repository describes it as "an open source alternative to ChatGPT that runs 100% offline on your computer", with downloads for Windows, macOS and Linux and local models pulled from HuggingFace (github.com/janhq/jan).
Open WebUI is a self-hosted web platform for AI chat that you reach from a browser. Its repository calls it a self-hosted AI platform built to run entirely offline, installed with pip, Docker or Kubernetes, and it adds multi-user access, roles, groups and per-group permissions (github.com/open-webui/open-webui). Both sit over the same model runners, so the choice between Jan, Ollama and LM Studio often comes down to how much you want to self-host (Open WebUI vs Ollama, Open WebUI vs LM Studio).
The real difference: a local app, a shared server, and a system that lands work
Jan runs the model on your machine. It is a desktop app for one person, so your prompts, files and chats stay on that computer, and it keeps working offline. Open WebUI is the opposite shape: one server your whole team opens in a browser, with accounts, roles and shared knowledge bases. It can also point at Jan's local API when you want to keep Jan as the model runner and add team access on top (Open WebUI's page on Jan).
Both are chat windows over your models. You type a request, the model answers, and the output stays in that window. Kortix targets a third job. It is the open-source AI Operating System: your agents, skills, memory and connectors in one git repo you own, with each session running on its own cloud computer and finished work landing through a change request a person approves. Kortix is the leading open-source alternative to Claude Cowork and ChatGPT Work.
Where a team outgrows both
Jan stays a one-person desktop tool. Open WebUI grows into a shared server, which is the right move when several people need one browser-based chat you self-host (Open WebUI for teams). Neither one is built to take a job, run it on its own machine, and hand back a reviewed change to your repo, which is what most teams mean by "work that lands".
When that is the goal, weigh the whole field on this site (open-source Open WebUI alternatives) or read the head-to-head (Kortix vs Open WebUI). Kortix runs on Kortix Cloud, in your VPC, or on your own on-prem network, and self-host is free (the self-hosting guide).