Castify

Two or three months into building Castify, before there was a product or a market or even a name, I was sitting in my bedroom testing an early version with my siblings. I typed ‘bruh moments of history’ into the prompt as a joke. The AI generated a podcast — one host, no co-host yet, just a voice talking about Archduke Franz Ferdinand’s wrong turn that started World War I, and Australia’s losing war against emus in 1932. We listened. We laughed for fifteen minutes straight.

That was the moment I knew. Not because the product was polished — it wasn’t — but because the experience was something none of us had ever had before. AI talking about historical absurdities in the rhythm of a comedy podcast was funny and engaging and it taught us something. I’d been building blind. That night I knew it would work. Someone, somewhere, would want this.

The early version of Castify was prompt-based — type something in, get a podcast out. Useful, fun, but not yet necessary to anyone’s life. The pivot came when I thought back to college. I’d had stretches where I’d miss a class and have to read three lectures of slides to catch up — six hours of work for what would have been a one-hour lecture if I’d just been there.

I built notes-to-podcast for the version of myself who was sleep-deprived in a UMass dorm trying to catch up before an exam. Upload your slides, get a 20-minute audio review, listen on a walk. That feature is what turned Castify from “fun toy” into “useful tool.” It was also what made the rest of the story possible.

I’d been building Castify for over a year at that point. Filed a provisional patent in December 2023. Spent the next year working a banking job during the day, building Castify at night, telling myself the next month would be the month it broke through. Twelve straight months of that. No co-founder. No outside money. No real signal any of it was going to work.

In December 2024, I commissioned a video from the most-followed student account on TikTok — a creator with over a million followers in the exact niche I needed to reach. The video showed what Castify could do: upload your notes, get a podcast out. It hit 17.8 million views in a week. It became the second-most-viewed video on that creator’s entire account.

There’s a thing about a moment like that I want to explain, because it’s misunderstood. The video wasn’t viral because of luck. It was viral because the product was genuinely new — people had never seen anything turn their study notes into a listenable podcast before, and the demo did the entire job in 15 seconds. Paid creator placement put it in front of an audience. The product did the rest. If Castify hadn’t been good enough, the video would have done what most paid sponsorships do: gotten 200K views and disappeared. Instead it outperformed almost everything that creator had ever made.

But viral attention is fragile. The viral moment generated maybe 15–20K downloads total before the attention cycle dropped off. That’s real, but it’s a spike — not a business. I had to lock in immediately — fix what was breaking under load, sharpen onboarding, build the subscription tier I’d been putting off. The viral moment didn’t make Castify successful. Capitalizing on it did.

What this taught me, and what I’d say to any founder reading this: distribution is now an open game. You don’t need a marketing budget that rivals a startup with VC. A bootstrapped solo founder can identify the right creator, fund a single piece of content, and reach an audience that would have cost a Fortune 500 company hundreds of thousands in 2015. But that only works if what you built is genuinely good. Distribution amplifies whatever you put in front of it — including your weaknesses. Build something real, then put it in front of the right audience, and the modern internet will do the rest.

Two weeks after the video hit, I gave notice at the bank. I haven’t worked a salaried job since.

The first revenue I ever made from a side project was the few weeks after the viral moment. Watching that come in — actual dollars, from people I’d never met, in countries I’d never been to, who paid for something I built alone — I can’t fully describe what that felt like. The closest I can get: it was the moment I realized I never wanted to do anything else with my life. Make money from anywhere, for something you built yourself, on your own terms. That’s the dream and I was living it.

Sixteen months later, Castify has over 70,000 downloads, paying users in 50+ countries with content generated in 70+ languages, and over $80,000 in lifetime revenue — built and operated entirely solo. The character system I launched a few weeks ago captured roughly a third of platform usage in the first two weeks with zero promotion. Paid conversion has doubled year over year. Revenue per install has doubled too.

I tell this story not because it’s exceptional but because it isn’t. There are good ideas in every founder’s head right now, and the path from “I’m building something” to “people are paying for it” is shorter than it has ever been. The barrier isn’t talent. It’s whether you’re willing to grind through a year of no signal.

Native iOS app from scratch. Multi-provider AI infrastructure routing different workloads to the most cost-efficient model for each use case. Document ingestion engine processing PDFs, slide decks, images, and links in under ten seconds. Subscription system with multi-tier pricing and continuous A/B testing. AI-powered character system with original and licensed voices. Daily content generation pipeline. ASO and paid acquisition across multiple international markets. Built and operated entirely alone — every line of code, every metric, every customer support email.

If you’re building something in this space — AI-native iOS apps, content-to-audio products, subscription apps with viral potential — I’m available for select projects. The version of Castify you’d hire me to build, but for your idea.

Email me at nate@natesullivan.ai.