Probably a good time to mention the CNCF Serverless Workgroup and the Serverless landscape. It lists all the Kubernetes-native Serverless frameworks as well as the proprietary ones.

OpenWhisk was one of the first projects in this space and is written entirely in Scala. Good to see a Kubernetes integration emerging.

https://medium.com/memory-leak/serverless-cloud-native-lands...

Other notable projects: Oracle's Fn, Bitnami's Kubeless, Platform 9's Fission, Iguazio's Nuclio and OpenFaaS (community project). (there are more)