The British Geological Survey has made SIGMA, the System for Integrated Geologic Mapping, available for free:
The BGS·SIGMA project (System for Integrated Geoscience MApping) is an integrated workflow for geoscientific surveying and visualisation using digital methods for geological data visualisation, recording and interpretation in both 3D and 4D…
BGS·SIGMA has … defined and documented an underpinning framework of best practice for survey and information management, which has then informed the design brief and specifications for an integrated toolkit. This toolkit enables assembly and interrogation/visualisation of existing geological information, capture of new data and geological interpretations, and delivery of 3D digital products and services. We have made the 2nd version of our award-winning digital field data capture tool available free with the expectation that geoscientists globally can use the system and share any modifications or developments in future BGS releases.
There is a catch, though – you’ll need to have ArcGIS and Microsoft Access installed on your computer. And it’s primarily intended for use with field-rugged tablet PCs. You can download SIGMA here.