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.
Propexo is a Boston-based proptech startup building the unified API and data platform for multifamily real estate. Often described as 'Plaid for commercial real estate,' Propexo lets software developers and property operators connect to 130+ property management systems - like Yardi, RealPage, AppFolio, Entrata, and Buildium - through a single, normalized API and no-code sync tool. What once took teams of engineers months to build, Propexo delivers in days, with standardized data models, webhooks, and enterprise-grade security. Founded in 2022 and a Y Combinator W2023 alum, it raised a $3.3M seed round led by Prudence in October 2023.
ngrok is developer infrastructure that puts any app, API, or AI model online with a single command. What began in 2013 as one engineer's weekend project to learn Go is now a unified ingress platform - reverse proxy, firewall, API gateway, and global load balancer rolled into one - used by more than 5 million developers and trusted by companies like GitHub, Twilio, Zoom, and HashiCorp.
Zapier is the automation platform that connects more than 8,000 apps so people can build workflows - called Zaps - without writing code. Founded in 2011 by Wade Foster, Bryan Helmig and Mike Knoop, the fully remote company has grown from a Y Combinator side project into a roughly $5 billion business serving millions of users, and it is now reorienting around AI agents that don't just move data between apps but make decisions inside the workflow.
Merge builds the connective infrastructure for modern SaaS and AI: one unified API that lets a product offer hundreds of HRIS, ATS, CRM, ticketing, and accounting integrations - and a newer Agent Handler that gives AI agents secure, observable access to thousands of third-party tools.