Low-cost porous paving materials and installation such as porous aggregate and recycled concrete sidewalk chunks or bricks are covered in Porous Paving by Bruce K. Ferguson and Rainwater Harvesting for Drylands, Volume 2, but for higher-traffic areas, or those where local codes require more durable or tested materials a few of the product options are listed below:
Invisible Structures, Inc.
Manufacturers of Gravelpave2 and Grasspave
Manufacturers of Geoblock
Uni Eco-Stone permeable pavers