Open Source Load Balancers
The load balancer is the one box every request passes through, which makes it both the single point that decides who your service even is to the outside world and the riskiest place to hand control to someone else's appliance or pricing. The open source load balancers and reverse proxies here sit at that edge on your own infrastructure, so routing, TLS termination, and how traffic is spread across backends are rules you write and can see, not a black box at your front door.
Caddy
Web server that provisions and renews TLS certificates for you, then reverse-proxies and load-balances
NGINX
Event-driven web server and reverse proxy that load-balances HTTP and TCP/UDP, and caches content
MetalLB
Gives bare-metal Kubernetes the LoadBalancer Services that cloud clusters get for free
HAProxy
High-performance TCP and HTTP load balancer that fronts demanding sites at L4 and L7
Seesaw
Google's LVS-based L4 load balancer that runs as a redundant two-node cluster with a floating VIP
Katran
Meta's L4 load balancer that forwards packets inside the kernel with XDP and eBPF
Keepalived
VRRP failover and IPVS load balancing that keeps a Linux service alive when a node dies
gobetween
Minimalist L4 load balancer that discovers its own backends from Docker, Consul, SRV, and more