xyConvert is a simple utility that converts files in formats supported by xylib into two- or three-column ASCII text file.
Output file can be read by (almost) any data analysis software as x,y points. The optional third column is for errors (standard deviations) of y.
Licence: GPL v2+
xyconvert is distributed with fityk, but it requires wxWidgets (wxGTK) >= 2.9, so it's not included in any distros yet. To compile it, you need to install wxGTK, boost and xylib, download fityk source and do ./configure && cd src/wxgui/ && make xyconvert.
You can download EXE file and run it (no installation).
not tested, but should work (after compiling with wxMac)
Linux:

Windows:

User interface is designed primarily for converting many files. That is why only a directory and a new extension for the output file(s) can be given.
It is also designed with reusability in mind - the same code (which is very small, less than 1KLOC) is also used as Open File dialog in fityk.
Marcin Wojdyr wojdyr@gmail.com
Don't hesistate to drop me a line if you have any problems with this program.