You pick n8n for a client project because it is open source, which in your head means free, no strings attached. You self-host it, wire up the client's CRM and inbox, and start billing them 400 dollars a month for "automation as a service." Six months in, you have five clients on the same model and a line item in your business plan that says "software cost: $0."
Then someone, maybe a lawyer, maybe a competitor filing a complaint, maybe just you reading the fine print at 1am, points out that n8n's license does not let you do that. Not the self-hosting part. The part where you turn around and charge other people to use your instance of it.
That gap between what "open source" sounds like and what the actual license permits is the thing every roundup of open source workflow automation tools skips. They rank n8n, Activepieces, Windmill, and a handful of others by connector count, UI polish, and GitHub activity, then move on. None of them open the LICENSE file. For anyone planning to build a client-facing automation business on one of these tools, our workflow automation team treats that file as the first thing to read, not the last.
TL;DR:
- "Open source" and "free to resell as a service" are not the same promise. Several popular tools are source available, not open source, and the difference decides whether you can legally charge clients to use your instance.
- n8n's Sustainable Use License lets you self-host and build internally for free, but offering n8n itself as a paid or hosted service to others needs a commercial license.
- Activepieces ships a genuinely permissive MIT license. Windmill and Automatisch split their code: an open AGPL core plus a paid enterprise tier for the features most agencies actually need.
- The infrastructure cost of self-hosting any of these is small. The license risk and the ongoing maintenance time are the costs the comparison charts leave off.
What "open source" actually promises, and what it doesn't
Open source has a specific legal meaning: the code is public, and the license grants broad rights to use, modify, and redistribute it, including for commercial purposes. A lot of workflow tools marketed as open source are not, strictly, that.
They are source available. The code is public and you can read it, audit it, and run it yourself. But the license attaches conditions, and the condition that matters most to an agency is almost always the same one: you cannot take the software and offer it to other people as a product or service of your own.
This is not a minor technicality. If your business model is "I host a workflow tool and charge clients a monthly fee for access to it," that is exactly the use case these licenses are written to block.
What each tool is actually built for
Before the license question, the five names that come up most in any search for open source workflow automation tools split into three different jobs.
- n8n targets general business automation with the deepest connector library of the group and a native AI-agent node, which is why most comparisons put it first.
- Activepieces copies the Zapier-style builder most closely: a visual, step-by-step canvas aimed at non-technical users who want something that feels familiar.
- Windmill is a developer platform first. It is built to run internal scripts, approvals, and data pipelines as code, with a workflow canvas layered on top rather than the other way around.
- Automatisch is the smallest and newest, positioning itself directly as a self-hostable Zapier alternative with a narrower connector list than n8n or Activepieces.
- Node-RED predates all of them and was built for wiring together IoT devices and hardware, which still shows in how it handles business-app integrations today.
Pick based on that job first. Then check the license for the specific thing you plan to do with whichever tool fits, because the license terms do not track neatly with how capable or popular the tool is.
The license nobody reads: n8n's Sustainable Use License
n8n is the tool that shows up at the top of almost every open source workflow automation tools list, and for good reason. It has the deepest connector library of the group and the most mature AI-agent node. It is also the clearest example of the gap this post is about.
n8n publishes its license directly in its GitHub repository. The Sustainable Use License on n8n's GitHub repo states that you may use or modify the software for your own internal business purposes, or for personal use, but you may only distribute it or provide it to others free of charge for non-commercial purposes.
Read that again from an agency's seat. Running n8n inside your own company, even to power a client-facing product you charge for, is fine. Standing up an instance per client and billing them for access to that instance is the thing the license is written to prevent, because that is n8n competing against its own paid cloud and enterprise tiers.
Where the other tools on every list actually land
Run the same check on the rest of the usual lineup and the picture gets more varied, not simpler.
- Activepieces licenses most of its codebase under MIT, confirmed in Activepieces' LICENSE file on GitHub, which permits using, modifying, hosting, and reselling that code without asking permission. The same file carves out two directories,
packages/eeand the enterprise API path, under a separate commercial license. In practice that means the core builder is genuinely resale-ready; a specific slice of enterprise-grade features is not. - Windmill is the strictest of the group once you read past the AGPL badge. Windmill's LICENSE file on GitHub grants free use of every feature in the Community Edition inside your own organization, but states plainly that you may not "sell, resell, serve as a managed service, modify or wrap" the Community Edition "under any form without an explicit agreement." Running Windmill as the backend of a paid client service is the exact scenario that line exists to block, not a feature-tier upsell.
- Automatisch keeps its core under a plain AGPL-3.0 license, with enterprise-only files (marked by an ".ee." naming convention) carved out under a separate license. Unlike Windmill, its public LICENSE does not add an extra clause banning resale or managed hosting on top of standard AGPL terms, which already permit commercial and SaaS use as long as you release your modifications under the same license.
- Node-RED, the oldest tool in this category, ships under the Apache 2.0 license through the OpenJS Foundation, a permissive license with no resale restriction at all.
So the group splits into three different answers to the same question, not one pattern. Activepieces lets you resell its core outright. Automatisch lets you resell its core if you are willing to share your modifications back. Windmill and n8n both require you to go sign a commercial agreement before you resell or host their community edition for clients at all. Treating all five as interchangeable "open source, so it's fine" options is exactly the mistake the feature-comparison roundups set readers up to make.
The cost nobody puts on the license page
Even once the license question is settled, self-hosting any of these tools is not free in practice, it is just cheap in a way that hides the real bill.
A single small instance of n8n, Activepieces, or Windmill runs comfortably on a 5 to 20 dollar a month VPS, as an illustrative range. Add a managed database, a queue for reliability, backups, and basic monitoring, and a production-grade setup for client work typically lands closer to 20 to 50 dollars a month in infrastructure, as an illustrative estimate in line with the cost breakdown in our guide to self-hosting n8n.
That part is manageable. The part that is not on any pricing page is the maintenance time: patching the OS, upgrading the tool without breaking a client's live workflows, and being the person who gets paged when a workflow silently stops at 11pm because an upstream API changed its response format. None of the five tools above eliminate that job. Open source just means you own it instead of a vendor.
Who should actually use these tools
If you are automating your own internal operations, the license question barely matters. Pick whichever of these tools fits your team's skill set and move on; n8n's connector depth and AI-agent node make it the default for most technical teams, which is also why it is our own default build platform.
If you are an agency planning to host one of these tools and charge multiple clients for access to it, the license is the first decision, not the last. Activepieces removes the question entirely. n8n, Windmill, and Automatisch all require either staying inside their free internal-use terms or paying for the enterprise tier that covers resale. Our white label services for agencies page walks through how agencies structure that build-you-sell arrangement correctly, licensing included, before it becomes a support ticket from a client's lawyer.
Key takeaways:
- "Open source" on a comparison chart does not guarantee you can resell the tool as a hosted service. Read the actual LICENSE file for the specific use case you plan to run.
- n8n and Windmill both cover free internal use but explicitly block reselling or hosting their community edition for clients without a commercial agreement.
- Activepieces lets you resell its MIT-licensed core outright; Automatisch's AGPL core allows resale too, as long as you release your modifications back under the same license.
- Node-RED's Apache 2.0 license carries no resale restriction at all, which is rare in this group.
- Self-hosting cost in dollars is small for all five tools. The maintenance time and license risk are the real costs, and they do not show up on a feature comparison.
