There is a go implementation of WireGuard with a fairly hefty warning at the top. [0]

There's also official documentation for how a userspace implementation should behave. [1]

The android version of WireGuard has a userspace implementation for devices without WireGuard in the kernel, which at the moment is pretty much all.

[0] https://github.com/WireGuard/wireguard-go

[1] https://www.wireguard.com/xplatform/