StackOne

StackOne is a London-based integration platform that gives B2B SaaS companies and AI agent builders a single unified API to connect to hundreds of enterprise systems - from HR and CRM to ticketing, messaging and identity. Combining a proprietary tool-calling LLM with a real-time, privacy-first engine, it offers 200+ pre-built connectors and thousands of ready-made actions so agents can reliably and securely take actions inside the software businesses already use. Founded in 2023 by Romain Sestier and Guillaume Lebedel, the company raised a $20M Series A led by GV (Google Ventures) in May 2025 and has surpassed 1 billion API calls.