ffmpeg supports both x265 and Kvazaar HEVC encoder

Tampere University of Technology has developed Kvazaar HEVC encoder since 2014. as LGPLv2.1-licensed open-source HEVC encoder. Their goals are

1. Coding efficiency close to HEVC reference encoder (HM)
2. Modular encoder structure to simplify its data flow modeling
3. Efficient support for different parallelization approaches
4. Easy portability to different platforms
5. Optimized encoding speed without sacrificing its coding efficiency, modularity, or portability
6. Reduced computation and memory resources without sacrificing its coding efficiency, modularity, or portability
7. Excellent software readability and implementation documentation

Like x265 being used in FFmpeg,

FFmpeg can make use of the kvazaar library for HEVC encoding.

Go to https://github.com/ultravideo/kvazaar and follow the instructions for installing the library. Then pass --enable-libkvazaar to configure to enable it.

It is also added in the Libav FFmpeg fork. It could be interesting to compare this to x265.