I'm not a Go expert so hard to judge, but:<p>github.com/rclone/rclone - Somewhat complex with abstractions, plugins, filesystems, networking, multi-platform support etc<p><a href="https://github.com/hashicorp/" rel="nofollow">https://github.com/hashicorp/</a> has a lot of Go
Go is self-hosting (<a href="https://en.wikipedia.org/wiki/Self-hosting_(compilers)" rel="nofollow">https://en.wikipedia.org/wiki/Self-hosting_(compilers)</a>) and not that old, so the source of the go compiler and its tools (<a href="https://go.googlesource.com/go" rel="nofollow">https://go.googlesource.com/go</a>) should be good examples (possibly not of all language features)