ATOM Download Services for access to pre-prepared data files can also be used in your own applications, the necessary operations are described in service metadata (xml document Service feed). For basic use (downloading files and receiving notifications about their updates), a normal Internet browser with the RSS Feed Reader add-on is sufficient.
Instructions for using the ATOM services feature to notify of data file updates are described in this document.

WFS and WCS download services for direct data access. Web services in OGC standards for issuing interactively created data files in the range specified by the requester using the BBOX function. Access without registration, technical limitation only on the number of elements downloaded once.

ArcGIS REST map services allow data to be downloaded using Queries.