To build Openbox from git you need:

A C Compiler (GNU GCC 3.2+ suggested)
-GNU Gettext 0.14.4
-GNU Autoconf 2.50+
-GNU Automake 1.11+
-GNU Libtool
-Xlib library/headers (devel package)
-Pkg-Config
-Glib 2.0+ library/headers (devel package) (http://www.gtk.org)
-libxml2 2.0+ library/headers (devel package)
-Pango 1.10+ library/headers (devel package)
-cvs or git or neither, depending on how gettext was installed*

Also you will probably want:
-Imlib2 library/headers (devel package)
-X Cursor library/headers (devel package)
-Startup Notification library/headers 0.8+ (devel package)

We recommend the latest versions of all these packages.

*) for versions below 0.18.1 cvs is needed, above that, see autopoint --version

Do the following to build and install Openbox in git:

% ./bootstrap
% ./configure
% make
su to root and
% make install
or
% sudo make install

Don't try running it from the openbox/ directory without installing, it won't
work. It needs to be installed before it is run.

The following commands will be available: openbox-session,
  openbox-gnome-session, openbox-kde-session, and openbox.

See the man pages for details about them.  If you want to run Openbox on its
  own, you probably want to run "openbox-session".



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In Ubuntu, you want these packages:

gcc
gettext
automake
autoconf
libtool
libpango1.0-dev
pkg-config
libglib2.0-dev
libxml2-dev
libstartup-notification0-dev
xorg-dev
libimlib2-dev

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