Before we dive in, quick word: everything you're about to read gets built, tested, and taken further inside Bestapps Academy, our Skool community. It's where we drop the actual skills, walk through the builds live, and troubleshoot each other's projects, so instead of just reading about a 3D hero, you ship one with people looking over your shoulder. If this guide clicks for you, that's the room where it goes from "interesting" to "in production."
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The software is already built. It's already free. It's sitting on GitHub right now — and the only thing standing between it and money is someone willing to deploy it and put a price on it.
That someone is you. Not because you're going to out-engineer a billion-dollar company — you're not going to try. You're going to do something smarter: arbitrage them.
Every tool below replaces a product businesses pay $100–$500/month for. Zapier. Calendly. Mailchimp. Salesforce. DocuSign. Except the open-source version costs you a $5 server and an afternoon. You're not selling software — you're selling the one thing the business owner will never do themselves: set it up, run it, and make it disappear into the background.
That gap is where the money lives. Here are ten of the richest gaps on the internet. Read to the end, then pick one and go.
01 — n8n
The Zapier killer that quietly funds entire automation agencies.
Zapier charges by the task and punishes you the second you scale. n8n does the same job — connect apps, move data, kill the manual glue work — except you host it and the meter never runs. Every business you know is drowning in it: lead comes in, gets copied to a CRM, triggers an email, generates an invoice, all done by a human, badly, every day.
The play: Automation agency. Build the workflow once, charge $1,000–$3,000 per build, then a monthly retainer to keep it running. Their volume can 10x and your cost doesn't move.
Start here: Deploy on a $5–10 VPS (Hetzner or Railway). Build ONE workflow for a business you already know — free. Screenshot the hours it saves. That screenshot is your entire sales pitch.
02 — Cal.com
Calendly's open-source twin that sells for $800 a setup.
Scheduling infrastructure you can white-label completely — your logo, their domain, zero "powered by." Every clinic, barber, tutor, and agency needs booking, and most are still doing it over text.
The play: Booking system in a box. Deploy it, brand it, hand it over. $500–$800 setup per local business, ~30 minutes of work once you've done it twice. Add a small monthly to keep it running.
Start here: Spin it up, connect a calendar. Do the first one free for a local business you like — trade it for a testimonial and a screenshot. Charge everyone after that.
03 — Plausible
Privacy analytics agencies quietly resell at $49/mo — per client.
Cookie-free, lightweight, and it makes the ugly GA4 dashboard look like a tax form. Agencies are done handing client data to Google; clients are done not understanding their own numbers. One clean dashboard solves both.
The play: White-label analytics-as-a-service. Host it once, brand it, resell dashboards at $49/mo per client. One server serves dozens — the margin compounds every time you add a site.
Start here: Host it, add a few sites you control. Then walk it into any agency you know: "your own branded analytics, no Google, flat monthly." They resell it up the chain; you keep the lights on.
04 — listmonk
Handles a million emails a month on a single box.
Open-source Mailchimp — except Mailchimp bills you more the second your list grows and never stops. listmonk doesn't care if the list is 1,000 or 1,000,000. Wire it to Amazon SES and delivery drops to cents.
The play: Managed newsletter service. A business paying $400/mo to email their list will happily pay you $200/mo to run it better — you pocket the spread, and it widens as their list grows.
Start here: Deploy, connect Amazon SES. Migrate one client's list, send their next campaign, show them the open rate. That's the whole demo.
05 — Twenty
The self-hosted CRM that ends the per-seat shakedown.
A modern, clean Salesforce/HubSpot alternative that doesn't charge $150 per user per month to store contacts. Small teams outgrow spreadsheets and slam straight into enterprise pricing. You're the way around that wall.
The play: Private CRM deployment + management. Setup fee to stand it up and import their pipeline, then a monthly retainer to run it. Their data stays theirs; the bill stays flat; you own the relationship.
Start here: Self-host it, build a sample pipeline to demo. Find one team drowning in a shared spreadsheet — that pain is your opening line.
06 — Chatwoot
Intercom and Zendesk in one inbox — used by 15,000+ businesses.
Live chat, email, WhatsApp, Instagram, Telegram — every customer message, one inbox, self-hosted. Intercom starts affordable and ends in a heart-attack bill. Chatwoot does the same job and ships with an AI agent (Captain) you can sell as "automated support" on top.
The play: Managed support desks. Stand up the inbox, embed the widget, wire the AI to their FAQs. E-commerce and SaaS teams pay setup + monthly for a support stack that costs a fortune off the shelf.
Start here: Host it, drop the chat widget on one client's site, feed Captain their existing FAQs so it answers the easy 60% on day one. Watch ticket volume drop, then price it.
07 — Documenso
The DocuSign killer that looks better than DocuSign.
Modern, TypeScript-built, open-source document signing — templates, audit trails, the full flow. DocuSign taxes you per envelope and treats data residency as a premium tier. Law firms, real estate offices, and agencies feel that every month.
The play: Branded e-sign setups. Deploy for firms that send contracts constantly, brand it as theirs, kill the per-envelope tax. Setup + monthly. "Your documents, your server, unlimited signatures" sells itself to anyone who's opened a DocuSign invoice.
Start here: Deploy, build one reusable signing template (an NDA or standard contract). Demo it to a single realtor or small firm — the savings close it for you.
08 — Medusa
The developer's Shopify — with none of the platform fees.
Headless, open-source commerce that scales past what boxed platforms allow. Every growing brand eventually resents Shopify's transaction cut and its customization ceiling. Medusa hands you a commerce engine to build anything on — and keep 100% of the sale.
The play: Custom store builds. Owned, fast, fee-free storefronts for brands outgrowing Shopify. $3,000–$10,000 per build plus a retainer. No percentage of revenue ever leaves for a platform again — that pitch lands hard with brands doing volume.
Start here: Spin up the starter, build one demo storefront for your portfolio. Find a brand paying Shopify's fees on real volume — do the math for them out loud.
09 — Mautic
HubSpot's whole playbook — without HubSpot's whole invoice.
Open-source marketing automation: email sequences, lead scoring, landing pages, campaign tracking. HubSpot does all of this and prices like it's the only company alive that can. Most SMBs collect leads and then do nothing with them because the tooling costs too much.
The play: Managed marketing automation. Run the whole engine for businesses that can't stomach HubSpot — build the sequences, score the leads, report the wins. $250+/mo per client. Retainer income that gets stickier every month.
Start here: Deploy, build one nurture sequence. Find a business collecting leads but never emailing them — turn their dead list into booked calls and let that result set your price.
10 — Supabase
The reason you can ship a full SaaS in a weekend.
Auth, a Postgres database, storage, realtime APIs — the boring, load-bearing 80% of every app. This is the Firebase replacement, and it's the one repo here that doesn't make you a reseller. It makes you a founder. The part that used to take a month of setup is done before you finish your coffee.
The play: Build and sell your own product. Micro-SaaS, client apps, MVPs — Supabase removes the backend excuse entirely. Ship the smallest thing someone will pay for, put a Stripe button on it, and you're in business. The others rent you a job; this one builds you an asset.
Start here: Create a project, wire up auth and one table. Ship the tiniest possible paid feature — one thing, one price. Don't build the empire, build the first dollar.
Your first 7 days: pick ONE
The biggest mistake you can make right now is trying to run all ten. That's not ambition — it's a way to do nothing slowly. Here's the version that actually works:
Pick the one that matches a business you already have access to. A friend with a shop. A cousin's agency. Proximity beats potential.
Deploy it this week. A $5 server and an afternoon. Deploy first, learn as it breaks.
Do the first one free. Trade a real setup for a testimonial and a before/after. That proof is worth more than the fee you skipped.
Charge the next one. Same work, now with proof. The second client is where it stops being a hobby and starts being income.
The developers making millions off these repos aren't smarter than you. They just moved first and picked one. You now have the list. The only variable left is whether you close this and go deploy something — or close this and forget it by tomorrow.
Now go build.