gretl will read various other data formats.
Plain text (ASCII) files. These can be brought in using gretl's "File, Open Data, Import ASCII…" menu item, or the import script command. For details on what gretl expects of such files, see the Section called Creating a data file from scratch.
Comma-Separated Values (CSV) files. These can be imported using gretl's "File, Open Data, Import CSV…" menu item, or the import script command. See also the Section called Creating a data file from scratch.
Worksheets in the format of either MS Excel or Gnumeric. These are also brought in using gretl's "File, Open Data, Import" menu. The requirements for such files are given in the Section called Creating a data file from scratch.
BOX1 format data. Large amounts of micro data are available (for free) in this format via the Data Extraction Service of the US Bureau of the Census. BOX1 data may be imported using the "File, Open Data, Import BOX…" menu item or the import -o script command.
When you import data from the ASCII, CSV or BOX formats, gretl opens a "diagnostic" window, reporting on its progress in reading the data. If you encounter a problem with ill-formatted data, the messages in this window should give you a handle on fixing the problem.
For the convenience of anyone wanting to carry out more complex data analysis, gretl has a facility for writing out data in the native formats of GNU R and GNU Octave (see Appendix D). In the GUI client this option is found under the "File" menu; in the command-line client use the store command with the flag -r (R) or -m (Octave).