Everything Hiew can do, Rizin[1] can do too, and is completely free and open source[2] under LGPL3 license. Moreover, it supports more architectures, platforms, and file formats, as well as GUI in Qt - Cutter[3][4]. If something is missing in Rizin but presented in Hiew, please let us know by opening the issue with details.
[1] https://rizin.re
[2] https://github.com/rizinorg/rizin
[3] https://cutter.re
[4] https://github.com/rizinorg/cutter