No can’t run custom OS as far as I know; without some seriously hackery. Admittedly UniFi NAS software currently is not nearly as feature rich and enterprise as TrueNAS for example, but it’s all very new. Ubiquiti has had a track record lately of iterating very quickly adding more and more enterprise features into their products. I expect to see more hardware offerings in the UNAS line soon as well. Highly recommend Ubiquiti! I have a complete setup at my house with their switches, routers, APs, and protect cameras. It’s awesome!