People keep saying AI coding agents can only build basic, cookie-cutter apps. I decided to prove them wrong. For my first major public demo, I spent some time pushing Replit ⠕ 's AI agent to its absolute limit. The result? I rebuilt macOS entirely on the web. No templates.... No imported UI libraries. 100% vibecoded using natural language. As the AI Chief of Staff at Replit, I spend my days building enterprise-grade platforms for our internal teams, but I wanted to see how far a solo developer could take a passion project just by talking to an AI. What’s inside: 💻 A functional VS Code replica with an integrated terminal and multi-agent AI copilot. 🔌 Custom MCP servers hooked up to fetch, PostgreSQL, Stripe, and GitHub. 🤖 A rebuilt "Siri" that actually controls the OS -changing wallpapers and opening apps via voice or text. 🕹️ Parallels Desktop running Windows XP, Ubuntu, and games like Mario Kart. 📱 AND... I asked Agent 3 to turn it into an iOS mobile app in one shot. It actually worked. The ceiling for software creation has been completely blown open with Agent 3. And 4 those who know... greater things are coming soon :) We are way past basic web apps. What are you building? 👇show more

Here's the iOS themed version which gets shown whenever this app is opened on an iPhone 📱

Special thank you to @zhenthebuilder for pushing me to make this video and @mattyp for advising me. and obviously @pirroh & @amasad for believing in me 🧡

@Replit How much did this cost you? I love Replit but find myself leaving the ecosystem because it’s gets very expensive very quickly

@Replit I’ll find the exact cost tomorrow morning but it was built pre cost optimization & was still <$100

@Replit Awesome! Curious to know the results I have been building quite extensively on Replit and have at few occasions been surprised at the cost (before the recent launch and optimizations!

@Replit Dog shit web slop buddy sorry

@Replit You’re too kind!

@Replit Yo chat, I think this guy is cheating. No way Replit can do all this

@Replit 100%

@Replit I just shipped the Clawberry

@Replit Love that!

@Replit Making it open source once it’s done tonight. Encrypted agentic communication device, agents can text - call - email - run commands.

@Replit This is incredible, but can it run Crysis? Seriously though … insane build!! 👏 🫡

@Replit I’m sure it could 🙃

@Replit That’s AMAZING!!! So far the most advanced vibe-coded solution I’ve seen! 🤩🚀

@Replit Thank you 🧡

@Replit This is nuts

@Replit Thank you!

@Replit Do you have a github for it? @agi2asi

@Replit I’ll post it soon

@Replit totally wild

@Replit 🙏

@Replit Amazing! I’d love to hear a little bit more about what agent mode you used most (e.g., lite, economy, power, or max), and what was the overall cost to develop?

@Replit This was done in ~3 weekends with today’s equivalent of Power autonomy. I do not usually recommend going into Max mode unless you’ve spent a considerable amount of time setting up your docs, architecture, and design systems

@Replit Incredible! 🤯 Build X Code as well and I’d pay to use it online!

@Replit Challenge accepted. Xcode 26.3 with copilot or prior version?

@Replit Dunno? As a PC user I currently don’t have either! You decide.

@Replit okay the custom MCP servers wired to PostgreSQL and Stripe is what takes this from cool demo to actual infrastructure. how's the Siri voice control working under the hood?

I’ll admit that I had to run numerous tests when I got it to work the first time cause I had a hard time wrapping my head around it. Gave agent the AwesomeMCP GitHub link and watched it plug most of them into it. Felt magical. Siri is powered by Realtime via WebRTC to help with latency. Going to upgrade it to 1.5 tomorrow and give it another spin

@somi_ai @Replit congrats you've already built a better Siri than Apple

Tbf, it doesn’t take much lol. I love the replica Siri so much that I’m now building a swift native replacement that’ll be powered by Realtime 1.5. All i really wanted was an assistant that could understand my intent instead of randomly calling the plumber when being asked what the weather will be like this afternoon

@Replit Wow

@Replit This is wild

@Replit Grazie friend

@samuel_spitz @Replit Well done that's epic

@samuel_spitz @Replit Thank you

@Replit Replit is the best coding agents I’ve use in my oinion

@Replit Couldn’t agree more

@Replit Tim Cook after looking at this demo:

@Replit 😂

@AndrewJDavison @Replit 👏🏽

@Replit Cool!

@Replit looks great - Mac os is a highly described system - I'm finding limitations is systems that are being invented.i.e. Are not highly described already. In this case I'm still having to think through the logic first myself and get the agent to iterate through it.

@Replit @grok what screensharing/screen recording software is he using?

@Replit This is wild. The real flex isn't the macOS replica - it's the MCP servers with Stripe/PostgreSQL/GitHub hooks. Most "rebuilt X" projects are visual clones. You actually wired infrastructure. Agent 3 + MCP is the combo that matters here.

@Replit the "no templates" part is the real flex here. building a full os environment just by describing it proves we're moving from syntax to pure intent.

@Replit Still amazes me to look back at my work from 2020-2021 and see how far LLMs have come. So much more on the horizon too.

@Replit 👏🏼👏🏼👏🏼🚀

@Replit DAMN! how did that cost bro. Opus???

@Replit Around $100 but I’ll get the exact figure

@Replit this is some inception level shiii

@Replit I’ll take some time to share a video of the copilot replica within VS Code replica building out a mini MacOS replica within this system. It’s very trippy to watch

@Replit 2 bad it lies & the backend is always incomplete & after stating everything is done correctly and charging every time @agi2asi @amasad @ReplitSupport due to ur agents fuckup, you guys made me lose a client that was going to pay me to make websites for all their co. costing$1000s

@Replit @amasad @ReplitSupport Have you submitted a ticket? If not, please do and let @ReplitSupport know so we can investigate

@Replit @amasad @ReplitSupport Along with your “agent” completely locking us out. Also your site said that we had to contact support and then I was told support could not help us?? This makes clients not want to use my services or you guys ever @agi2asi

@Replit @amasad @ReplitSupport @amasad @ReplitSupport

@Replit BLOWN AWAY

@Replit I am positive that this code is not exportable, it can’t scale and outside of the specific backend Replit runs on—this would crash or fail to run on any other system. OS-level architecture is complex and difficult for a reason.

@Replit It actually is. I’ve exported it and run it on a very old Lenovo T450, a modded Pi 5 and an older MacBook Air. Happy to demo that if the community is interested. Total size is <500MB with all the modules. Considerably smaller prior to installation.

@Replit Absolutely, you would need to show the hardware and then you going through the fresh install process.

@Replit No problem

@Replit These fucking regards won’t sto pushing their tools ahahah

@Replit Don’t mean to push another tool here but I hear Grammarly is pretty lit

@Replit This is why Apple released the new MacBook Pro this morning with such excessive power. Agentic control baked into the OS controlling EVERYTHING, with a custom Apple LLM running locally. With deep Siri control.

@Replit this is impressive

@Replit Thank you

@Replit 🤯 @Jason

@Replit 这才是AI该有的样子

@Replit Thank you 🙏 This is my first attempt at posting a full fledged demo and the encouraging words mean the world

@Replit Meh

@Replit Appreciate you