Cornerstone · reference architecture
The Open GTM Stack
Everything the rented stack does — HubSpot, Marketo, Klaviyo, Segment, Clay — rebuilt on open tools you own, hosted in Europe. This is the kind of engine we deploy. The exact picks depend on your situation; the principles don't.
Every box in the standard go-to-market stack now has a credible open or fairly-priced alternative. Below is the reference architecture we work from — what each layer does, the open tool we reach for first, what it replaces, and roughly what it saves. Treat it as our opinion, not gospel: on a real project we'll choose based on your scale, your team, and your constraints.
The map
What replaces what.
Each layer: the open tool you own, replacing the rented tool you used to pay for. The orange edge marks what's yours.
Privacy-first traffic insight—Lightweight, GDPR-clean, no data sold.
Behavioural / funnel analysis—Self-hostable, full funnel + session replay.
One clean source of truth—Data in your warehouse; 350+ connectors.
Contacts, companies, pipeline—Flexible object model, no per-seat gouging.
Nurture, scoring, journeys—Most mature open MA; full nurture + scoring.
Campaigns + transactional—Millions of sends on tiny hardware, no per-contact tax.
Capture + feedback—No-code, self-hosted, full analytics.
A/B and feature flags—Test without enterprise pricing.
Wire it all together + AI—Self-hosted automation, AI steps, no task tax.
Booking without the leak—Open, embeddable, yours.
See it all in one place—Clean SQL-or-clicks reporting on your data.
Run it on your terms—Sovereign by default, subject to EU law.
Hover or tap a layer for the why. Illustrative reference architecture — final picks depend on your situation.
The arithmetic
What it costs you vs renting
We won't put fake numbers on your situation. But the shape is consistent: the rented stack is a monthly bill that grows with your success — more contacts, more seats, more sends, more money. The owned stack is a build cost (once) plus modest hosting (flat). The crossover usually arrives faster than people expect, and after it, the gap widens every month you grow.
More importantly: the data is yours, the exit is free, and nobody is skimming margin on the setup.
The objections
"But who maintains it?"
Fair question — it's the real objection. Three answers:
- 01 We document everything and train your team, so day-to-day operation doesn't need us.
- 02 Where you want a hands-off arrangement, the stack runs on managed European hosting and we (or your team) maintain it on a defined basis — no mystery, no lock-in.
- 03 These are mature, widely-used tools with real communities behind them — not someone's weekend project. Tens of thousands of teams run them in production.
The honest trade-offs
We'd rather you trust us than oversell. The owned stack isn't free of cost — it's a different cost. You trade a predictable rising rent for an upfront build and ownership. Some rented platforms have slicker onboarding or a specific feature an open tool doesn't match yet. We'll tell you when renting genuinely wins for a given box — sometimes it does, and we'll say so. The point isn't open-source purity. The point is that you should decide what you depend on, with the full picture — not get defaulted into a cage.