01
A working app.
Real screens, a real URL. It works, and you built it yourself.
One day in.
One decision out.
Find out if your idea is worth a quarter, in a day. No dev team, no code.
Free community evenings across Europe · Pro days for seniors · In-house days for teams · Get the free playbook · Excellent on Trustpilot, 4.6/5
MVP build is cheaper by
99%
Building got cheap. Deciding got hard.
Your backlog is full of ideas and short on evidence. The sales ask, the CEO's pet idea, the redesign everyone believes in, all untested, because testing used to need a dev team and a sprint budget.
One of Jason Calacanis's people built an intranet on Lovable for under $2,000 in four hours. He said it would have cost $500,000 two years ago. (Source)
Product Build Day puts the decision back in the room.
What you leave with
By 17:00, you have these
02
Feedback the same day.
Real users or synthetic testers try it while you watch. Reactions, not results.
03
A decision.
Go, pivot, or stop, in front of the evidence. An idea that cannot survive a day is not worth a quarter.
Voices
“If you want to build sth real in 6 hours, while meeting cool like-minded people - do it! It will be worth your time.”
Tomek Rusiłko
Digital Product Leader, Lunar Logic
“Great experience! We built a working MVP in a day, collaborated well, and learned a lot about rapid AI-assisted product development.”
Aliaksandr Astapchyk
Software Engineer (Frontend & Full-Stack)
“It became clear to me that spinning up several working MVPs of the same idea — each implemented differently, with a different preset of features and design — is a genuinely fast task, and one that helps you figure out much earlier, right at the brainstorming stage, what actually belongs in the final version. I'm definitely adding this to my toolkit.”
Yevhenii Harychev
Product Engineer, ScanExpense
Formats
Pick your day
The free community evening. Three hours, one challenge for the room, revealed on the night.
3 hoursUp to 16Free
Build it. Test it. Pitch it. One-day training in Berlin on 26 November 2026.
8 hours24 seats€690
A private day inside your company, on your riskiest roadmap bets. On your site.
8 hoursUp to 20From €5,900
What is next
Where the next rooms are
- 7 October 2026🇷🇴 BucharestGuest sessionSee details →
- 27 October 2026🇵🇱 WarsawFreeSee details →
- 26 November 2026🇩🇪 Berlin
ProSee details →
The evenings are free, by application, English. Pro days are paid. All events →
Proof
It already happened, more than once
The brief
“How might we help a returning 25-year-old Zara shopper open the app at 7:45 a.m. and choose a complete outfit from her saved looks and today's feed in under 90 seconds?”
A user, a moment, a goal.
The actual brief from Thessaloniki. 31 words. Name those three and it can be built and tested in a day.
Run your own.
The playbook is free.
The Facilitator's Playbook. 112 pages, Creative Commons. The schedule, the challenge template, the judging sheet, the pitch format, and every mistake I already made so you do not have to.
Get the PDF
Who runs it
Marcin Klimaszewski.
Founder and facilitator.
- 15years in product and UX
- 100+workshops across Europe
- 2ndat TechArena Sweden 2026, solo, against 90+ people, with this exact format
I would not sell you a day I have not bet on myself.
Three formats.
One decision.