Log shipping is a feature that replicates a database by taking regular incremental backups, transporting them files and restoring on a destination server. The destination database can be accessed in a read-only mode.
This is commonly used for off-site backup or reporting purposes, so that heavy reports can be run against the destination database rather than adding load to the praimary (usually customer facing) server.
The destination database can be accessed as a read-only database during the gaps between the database restore.
This technique is supported by Microsoft SQL Server, 4D Server and PostgreSQL.