ClosedXML 0.68 or better can read/write xlsx files fine for Excel 2007 or better. Free spreadsheets would be best for my needs if they could interoperate with ClosedXML. Does one exist that simply works bidirectionally with ClosedXML? My reading of the situation:
OpenOffice can't write xlsx.
Gnumeric 1.12.8:
It could open a simple file created by ClosedXML and the sheet name was correct but all cells were empty.
A simple file originally from Excel, and saved fresh from Gnumeric, then read in by ClosedXML, ended up causing an exception from ParseInt32(null).
Planmaker (v679) failed to open a simple file from ClosedXML ("unknown file format") yet it succeeded opening an Excel output file.
I wish some spreadsheet would base its code on ClosedXML.
OpenOffice can't write xlsx.
Gnumeric 1.12.8:
It could open a simple file created by ClosedXML and the sheet name was correct but all cells were empty.
A simple file originally from Excel, and saved fresh from Gnumeric, then read in by ClosedXML, ended up causing an exception from ParseInt32(null).
Planmaker (v679) failed to open a simple file from ClosedXML ("unknown file format") yet it succeeded opening an Excel output file.
I wish some spreadsheet would base its code on ClosedXML.