Building Ossmo: How I Built a Multi-Model AI Workspace with 75+ Models

I recently launched Ossmo — a unified AI workspace that aggregates 75+ AI models from 15 providers. Try it free: https://ossmo.sbs

The Tech Stack
Frontend: Vanilla JS + Tailwind CSS
Backend: Cloudflare Workers
Database: Firebase Firestore
Auth: Firebase Auth (Email + Google)
Storage: Cloudflare R2
Payments: UPI QR + Google Apps Script verification
Why Vanilla JS?
I chose vanilla JavaScript over React/Vue because:

Performance: No virtual DOM overhead
Bundle size: <50KB total JS
SEO: Server-rendered HTML, fully crawlable
Simplicity: No build step, just deploy HTML
The AI Model Layer
Ossmo routes requests to multiple providers:

const MODEL_PROVIDERS = [ { id: "openai", name: "OpenAI" }, { id: "anthropic", name: "Anthropic" }, { id: "gemini", name: "Google Gemini" }, // ... 12 more providers];
Each provider exposes 4-7 models, giving users 75+ choices.

UPI Payment Integration
For Indian users, I built a UPI QR system:

Generate unique order ID
Add unique paise (₹0.01-₹0.99) for verification
Show UPI QR (Google Pay, PhonePe, Paytm compatible)
Poll Firestore for payment confirmation
Credit wallet on confirmation
This avoids expensive international payment gateways and works
with every Indian UPI app.

Free Tier Strategy
Free users get:

15 messages per day (rolling 24-hour window)
Access to Free Models (GPT-OSS 120B, Qwen 3.8 27B)
Reasoning effort controls (Low, Medium, Max)
All workspace features
This gives users real value while protecting premium model costs.

Try It
If you're interested: https://ossmo.sbs

Free forever plan, no credit card needed. Premium plans start
at ₹249/month with UPI billing.

Founder of Ossmo. Reach me at [e-mail]