Intel has released an open source AV1 video encoder called "SVT-AV1". It's designed for really beefy, real-time CPU encoding and because of this the system requirements for 4K encoding is 112 logical CPU cores and 48GB of RAM.

It's really nice to see that we now have three competing encoders.

The reference aomenc encoder (currently provides the best looking results, but is really slow)

Xiph/Mozilla's Rav1e encoder (focused on speed)

Intel's STV-AV1 encoder (to be determined how good it is)