Right, I've had a quick look and without getting into compiling PDO
drivers etc, you should find you can get Habari working using sqllite
as follows:
1. Enable PHP support by uncommenting the following line in
/private/etc/apache2/httpd.conf:
LoadModule php5_module libexec/apache2/libphp5.so
2. Restart Apache (System Preferences > Sharing and unselect and
select Web Sharing).
3. Install Habari as per the Habari instructions for sqllite.
By default Apache on OSX is configured to use
/Library/WebServer/Documents for the document root of the server and
the Sites directory for users, so you'll need to extract the Habari
source to one of these locations.
Each are accessible via
http://localhost/ and
http://localhost/~username/ respectively.
This should hopefully get you heading in the right direction of a
basic functional install on your local system.
Things get more complicated when trying to use another DB type as PHP
on OSX only comes with the PDO driver for sqllite, so you need to
compile the PDO driver for the other DB types (It'll take a bit longer
to document this procedure).
The Habari requirements also detail GD (which isn't enabled on OSX
either), but my installation seems to be working fine without GD
support. Maybe someone else could provide more insight into why GD is
required.
HTH
Colin