Tesser is a cloud development runtime for developers and coding agents running more than one environment at once. Its CLI gives every git worktree a dedicated Linux VM, syncs the local checkout over SSH, and starts the app with the install and dev commands already in the repo. Dev servers, builds, and tests run on that machine, and ports forward back to the laptop, so the app still opens at localhost:3000 with hot reload and sign-in cookies intact. Editing stays on the laptop. The machine runs the files in the editor, and most stacks start without a Dockerfile or devcontainer. The launch is aimed at teams running several agents across branches at once. Claude Code, Codex, and Cursor can call Tesser from the laptop, and cloud agents such as Devin use an API token to reach the same machines. Each agent gets its own worktree and VM, so those runs do not share port 3000 or the laptop CPU. A reviewer can open the running branch from a preview link, and each branch can keep its own Postgres and Redis. Default machines are Ubuntu 24.04 with Node, Bun, and Docker, at 2 vCPU, 8 GB of memory, and 40 GB of disk. You pay for the seconds a machine is awake, and only for its disk while it sleeps. Machines fall asleep after 10 idle minutes, or after 2 hours if a dev server is running. Teams can move every machine into their own AWS account, inside their VPC and on their own bill, and leave only the control plane with Tesser. The company is in Y Combinator's Winter 2027 batch and launched before the batch started. CEO Jeffrey Lin was previously a founding engineer at Fleetline (YC S25). CTO Rohan Godha was a software engineer at Mintlify and founded Brainrot.mov, which was acquired.