Can be everything you want, i know only this Delphi component for this kind of work (http://www.solfs.com/index.html) and look like a kind of database because have transactions.

However, maybe not so common in FoxPro but is possible load a file in a stream and operate on it, and this meaning, the file is in memory. Also, the most easy in fox is load the file in a string (not the most effective) or use a ADO RecordSet and built the field description in the fly, and put some Blob field for store things. Maybe this is the cheap & easy way in Fox for do this...