Galera Load Balancer
GLB is a TCP load balancer similar to Pen. It lacks most of advanced Pen features, as the aim was to make a user-space TCP proxy which is as fast as possible. It can utilize multiple CPU cores. A list of destinations can be configured at runtime. Destination "draining" is supported. It features weight-based connection balancing (which becomes round-robin if weights are equal).
Galera Load Balancer (glb) is maintained as open source project in freshmeat site: glb