Postarc connects ArcMap with PostGIS databases.
It enables read and write access to PostGIS-powered Feature Layers.

Postarc is Free Software licensed under the terms of the 
GNU Lesser General Public License (LGPL).

Postarc is written in C#. You'll need Microsoft Visual Studio 2010 and
ArcGIS 10 SDK for .Net to compile it and ArcMap 10 to run it.

The connection to PostGIS/PostgreSQL is handled by the Npgsql 
library which is not part of this distribution.

Note: Postarc is work-in-progress and not really useable by now.