From Lazarus wiki
fileutil is a Lazarus unit that:
- provides file/directory handling functionality both for the Lazarus IDE itself as for normal developers
- provides UTF8/Unicode alternatives to the FPC RTL functions with the same name (these functions are currently being moved to LazFileUtils unit, and "inlined" in FileUtil).
When a stable FPC is released that has full Unicode support, the latter functionality can presumably be stubbed out.