The String Replace app simply does what the name says: it replaces strings in incoming textfiles, private data or attached metadata.
You could use this app for example to replace some strings in an incoming XML file, without having to write a complete XSLT.
In version 2 support for a text-encodings is added.
In version 3 support for a different separator-symbol is added.
In version 4 support for a metadata and private data is added.