Forge is a tool that enables simultaneous development of multiple services within a single cluster, allowing developers to isolate their work and integrate test with other services. This approach uses a shared cluster, where each developer deploys their own unique version of the service, preventing collisions and enabling independent testing. Forge achieves this through a `service.yaml` file, which defines the deployment settings for each service, including a unique name and preview URL. By using Forge, developers can run dev versions of the same service independently, without affecting other services in the cluster.