You can download official releases of Wicked Engine from Steam with auto-update functionality:

Official Wicked Engine and related releases on Itch (portable, no install required):

You can download the latest version of the Wicked Editor development build here (needs Github sign-in to download build artifacts):

You can read or download the PDF documentation of the Editor here:

The source code is hosted on Github (using this allows C++ development)
The C++ documentation can be read on Github
The LUA scripting documentation can be read on Github