We built this because we run GPU workloads across 22 AZs and most are idle most of the time. NAT Gateway would have cost us ~$792/month for AZs that mostly do nothing. Always-on NAT instances (fck-nat, which is great) were closer but still felt wasteful. nat-zero starts a NAT when a workload appears in a private subnet and stops it when the last one leaves. Idle cost is ~$0.80/AZ. Happy to answer questions.