Nightly builds are now available for download.
On some versions of OS X El Capitan, you need to apply workarounds. There are also several known incompatibilities between open-source WebKit and Safari. Please be aware of these before filing bug reports.
Safari extensions are incompatible with nightly builds of WebKit, and may cause crashes or incorrect behavior. If you encounter such behavior, please disable Safari extensions.
Windows Users - At this time you must also have the Safari web browser installed. You can then run the nightly build of WebKit by running the file 'WebKit.exe'.