After a year of development, Python Web Processing Service (PyWPS) 2.0.0 is available with a new stable release, which fixes a lot of bugs and instabilities from the previous 1.0.0 version, as well as add a lot of new functionality.
PyWPS implements OGC Web Processing Service 0.4.0 standard . It is developed with native support for GRASS GIS , however, it can be used with other GIS command line tools too (PROJ, GDAL/OGR, …), as well as with the R Project for Statistical Computing.
OGC Web Processing Service specification provides client access across a network to pre-programmed calculations and/or computation models that operate on spatially referenced data. The calculation can be extremely simple or highly complex, with any number of data inputs and outputs. It does not specify the specific processes that could be implemented by a WPS. Instead, it specifies a generic mechanism that can be used to describe and web-enable any sort of geospatial process.
Several client applications can be used with PyWPS, e.g. Embrio project  and there is also plugin for OpenLayers .
New development should be focused at implementation of the OGC WPS 1.0.0 specification.
Jachym & PyWPS Development Team