A signed Soundflower (as required by Apple, this version of Soundflower.kext will be installed in the /Library/Extensions folder, not in /System/Library/Extensions as previous versions were). Note that the Soundflower extension is signed, but the installer is not -- you will most likely have to hold the control key down to open the Soundflower.pkg installer for the first time.
The installer will ask for a password. This must be an admin password. If the installer is failing, some people have had success by using the installer with the root password. Please read this page for instructions on enabling root access: https://support.apple.com/en-us/HT204012
IF INSTALLING ON HIGH SIERRA
The first attempt to install will display a security alert, then fail. Afterwards, you need to go into System Preferences "Security & Privacy - General" pane and give permission to allow the install signed by the developer "MATT INGALLS". After giving permission, you will be able to run the installer successfully.
NOTE: This is only the Soundflower kernel extension. The SoundflowerBed app is retired. A new replacement is in the works. In the meantime, you can take your chances with an older version of Soundflowerbed, but you can do a lot with a Multi-Output Aggregate Device. Here's an example:
Say i want to play some audio in iTunes, but record it in Quicktime while listening to it out of the built-in speakers. Here is how i would set it up:
start playing audio
Open Audio MIDI Setup: (found in /Applications/Utilities)
hit the '+' button in the bottom left corner and select "Create Multi Output Device"
in the the panel that appears on the right, select "Built-in Output" AND "Soundflower (2ch)"
then hit the button with the gear icon bottom left and select "use this device for sound output" (you should still be hearing your iTunes output -- it is now going to both Soundflower and the built-in speakers)
Then In Quicktime:
create a new audio recording
in the popup menu next to record button select "Soundflower (2ch)" as the input
(you should now see record levels changing)