As everyone knows, Excel provides no way to control line spacing in "wrapped text" cells. The only answer would be to use a font which has less than usual "leading" (if that is the word) built in. Does anybody know of one?

Sorry. I didn't mean to sound silly. I should not have said "everyone knows", but it is a very common complaint and I was getting very frustrated by it. :(

i'm working on a computer all day long but i'm never using excel

You seem to know it's a "very common complaint", i guess you visited some MS or Excel forums ?
They have no answer about fonts you might use ?

I have scanned every Excel forum I can find, and looked at a lot of fonts. All the font producers seem to assume (perfectly reasonably) that one's software will handle vertical spacing. Every response on excel forums says "Excel does not provide any way to adjust in-cell line-spacing".

I use Excel as a project management tool, and like to have large tables which are regularly sorted by row, with cells in which the text is wrapped. The in-cell line spacing defaults to a much-too-spacious setting. The only way to reduce it is to use multiple rows in excel, but I cannot do that if I want to sort by row.

It seemed to me that, if one cannot use the software to fix the issue, perhaps one could find an unusually vertically squashed font that would achieve a similar (albeit clunky) result?

Can you show an image of what you want AND you do not want?

Not sure how to show an image. Does the forum allow uploading of a screenshot?

I have put a screenshot up on Imgur:

http://i.imgur.com/mGmxzUL.png

"Verticaly compressed" means that you want estended font ? like that (for example) : http://www.dafont.com/extra-large.font

I don't think that is the issue. I want less "leading" - which as I understand it is the vertical spacing automatically added by the font to separate lines from each other. Certainly it would also be good to have small "ascenders" and "descenders" (forgive me if those are not the right terms), but overall I want something which does not look too different from Arial, but behaves as though one had reduced the line spacing below 1 - which is, of course, perfectly possible in every MSOffice program except Excel.

What you wanted done is to decrease the line height. Since you mentioned adjustment for leading is not available in Excel, then you have to find another font or modify the line height of the current font. You can play with the fonts vertical metrics to get that done. I am not fond of touching other people's fonts so I could not help you on that matter.

BTW this will work fine on a Mac but will likely result to cropped ascenders and/or descenders and missing accents in Windows. I am on Windows so I do not know how MS programs behave on a Mac.

To compress verticaly or to extend horizontaly, it's the same. It's juste to change the ratio of the letters.
The difference is juste a question of size. You get an extended font, you reduce the size (Excel can change the font size) and it will look like a vertical compressed font.

So, it's easier to look for an extended fond (it exist many) to solve your problem.
Use the option "Show variant" for the search on DaFont.

A font with a relative large x-height in combination with a relative low line gap will do the job. Try something like the Optificio