FEX-Emu is a usermode x86 and x86-64 emulator, supporting arm64 and x86-64 hosts. It is similar to qemu and box86, though it follows a different approach, using an SSA based IR.
My contributions have focused around performance and compatibility, as I love optimization problems and solving bugs.
FEX is currently in a state where it can run several 64-bit applications, including being able to build itself. At the time of writting this, 32-bit support is still an uphill battle, but things should improve soon.
For more information check the FEX-Emu site!