Yes, I was the original core dev of StreamAlert during my time at Airbnb.

I'd say the biggest differences are that Panther:

- Has a UI-driven workflow (vs CLI)

- Has an improved design to be more scalable and cost-effective

- Is written almost entirely in Golang

- Made a larger investment in the Athena side, allowing data pivoting and correlation across types

- Has first-class support for monitoring infrastructure as "resources", opening up more compliance use cases

We applied a lot of lessons learned from running StreamAlert and from my team's experiences at Amazon.