“An open source stack to run a construction project” sounds ambitious. Not that much: the functions a construction project team needs exist today in open source, mature, and deployable on local infrastructure. What is sometimes missing is the integration layer, and that happens to be our trade.
What follows is not exhaustive. It is the toolbox we actually install, layer by layer, with the real alternatives. Nothing ideal on paper: things already in production, on projects you may know.
Layer by layer, what we install
| Layer | Open source tool | Replaces |
|---|---|---|
| Scheduling & coordination | OpenProject · ProjectLibre · GanttProject | MS Project · Primavera P6 |
| Site document management | Nextcloud · Seafile · Paperless-ngx | SharePoint · Box · Dropbox Business |
| Team messaging | Mattermost · Element (Matrix) | Slack · Teams |
| Meetings and video | Jitsi Meet · BigBlueButton | Zoom · Google Meet · Webex |
| Transcription | Meetily · Whisper | Otter · Fireflies · Read.ai |
| Notes & wiki | Obsidian (+ plugins) · Logseq · Outline | Notion · Confluence |
| Local LLM | Ollama · llama.cpp · LM Studio | OpenAI · Anthropic · Mistral API |
| RAG (augmented search) | Verba · Quivr | OpenAI Assistants · Glean · Mendable |
| BIM / CAD | FreeCAD · BlenderBIM · BIMServer | Autodesk · Bentley · Trimble |
| Database | PostgreSQL · SQLite | Oracle · SQL Server (on the app server side) |
| CRM (sales) | EspoCRM · Twenty | Salesforce · HubSpot |
On a large project you do not use everything: you take what serves. But the range is there, and every line is one SaaS dependency fewer.
Where it runs
A recurring question: “But where do we install all this?”. The answer is not one server, nor a single cloud. It is a local, tailored architecture, sized for the project.
Case 1 · Small project, short operation (10 people, under 12 months)
A single compact computer in the site offices is enough. It runs a local LLM, an augmented search engine and PostgreSQL. On cost: one desktop computer bought once, no licences, half a day of training.
Case 2 · Mid-size project (50 people, 24 months)
A compact computer on site plus a small Linux server (Hetzner, OVH or a self-hosted data centre) for Nextcloud, Mattermost and OpenProject. The central server sits in Europe, in France when it matters. Bandwidth is not an issue on a European site.
Case 3 · Large project or consortium (200+ people)
A distributed architecture: one central server per design and supervision team or main contractor, a compact computer on each major site, with federation possible between the Mattermost and Nextcloud instances. This is where framing is needed, but the technology is mature and nothing is being invented.
Open source is not a utopia for developers. It is simply the infrastructure we should never have stopped using.
The cost, compared
Comparing the cost of an open source stack with a SaaS stack is delicate: SaaS bills a visible cost (per user, per month), while open source asks for installation and maintenance time. But over 24 months, on a project of 50 people, the gap is structural:
- The usual SaaS toolbox (MS Project + SharePoint + Teams + Otter + ChatGPT + Salesforce): one subscription per user per month, for each block, running as long as the project.
- The self-hosted open source toolbox: infrastructure billed as a whole rather than per user, the initial installation time (three to five days for the first setup) and regular maintenance, on the order of one day a month.
Over two years and fifty people, the first cost grows with headcount and the second does not: that is where the gap opens. But it is not the only benefit. Open source also gives you:
- Control of the data. It does not leave your infrastructure.
- No lock-in. You can migrate, export, modify.
- Auditability. The code is readable, verifiable, certifiable.
- Continuity. No risk of a vendor raising its prices or dropping the product.
The real limits
Let us be honest: not everything is perfect in open source.
The user experience is not always at the level of a commercial SaaS. Mattermost is rougher than Slack. OpenProject asks for a little learning where MS Project is familiar. Nextcloud is less smooth than SharePoint on certain workflows.
Support is community-based: powerful, but asynchronous. For critical incidents you either take a paid support contract with the open source vendor (Nextcloud Enterprise, OpenProject Cloud Edition and the like), or you share one with a provider who knows the stack.
Integration between tools is not plug and play. That is where many IT departments give up and go back to an all-in-one SaaS. It is also where we bring value: connecting the blocks to one another is our trade.
How to start, without doing it all at once
The classic trap is wanting to migrate everything at the same time. Bad idea. The sequence we advise:
- Month 1 · Transcription. Replace Otter with Meetily or a local Whisper. Little friction, immediate gain, value you can show.
- Months 2 to 3 · Messaging. Deploy Mattermost alongside Teams or Slack. Move a pilot project onto it.
- Months 4 to 6 · Site documents. Nextcloud in parallel with SharePoint on a test project. Then assess.
- Months 7 to 12 · Scheduling. OpenProject on a pilot project. Keep MS Project on the others during the transition.
- Year 2 · Local AI. Once the infrastructure is stable, deploy the local LLM, then augmented search.
At every step you keep a way out: if a block does not suit the real use, you go back to SaaS on that scope. No dogma.
A closing word
What makes open source viable in 2026, and did not in 2018, is three things: the open-weights AI models have caught up, local hardware has become very powerful for very little (a compact computer is enough), and the open community has produced mature tools across every scope.
What remains is the wiring: who talks to whom, how, and in what order. That is what we install: not a product, an architecture chosen for your context.
If you want to see what this looks like in practice on a site, Cabestian OS is the demonstration. And the community page lists the blocks we admire and deploy most often. To discuss it on a specific project, booking a call is there for that.