Fluxbox builds on Blackbox source but has different goals.
For copyright see COPYING

Compile and Install:

# ./configure 
# make 
and then as root
# make install

for KDE slitsupport: 
 ./configure --enable-kde

To disable tabs and/or iconbar just  change it in configure menu.

To use your own configuration:
Create a directorory, in your homedir, called .fluxbox
and copy: init, titlebar and menu from fluxbox datapath.
Dont forget to change session.menuFile and session.titlebarFile
in the file init.

You can use your old blackbox configuration file too. Just copy
.blackboxrc to ~/.fluxbox/init . The same goes for menu file.
The bbkeys config file can be selected in the file init:
session.keyFile: <filename here>
You can also use the Blackbox themes in Fluxbox.
If there isn't any format for the tab in the theme then
the tab will have the same theme as the titlebar.

Thanks:
Blackbox team
#linux.se@dalnet, #linux.se@openproject.net
skypher of openprojects for buggtesting and providing fluxbox with themes: 
Clean CleanColor Makro, Carbondioxide and MerleyKay.
skarin, Perc, xfs, skypher and skywarper for buggtesting