Acorn 4.5.2 is almost ready to go- but I've just put up a new build with a tiny new hidden pref you can set with Terminal:

defaults write com.flyingmeat.Acorn4 wideKernSpacing 1

What this snippit does is expand the range of the Kerning slider in the text palette to -200 to +200. Depending on the font, a negative kerning will stop somewhere between -30 and -22, but without this pref Acorn will automaticaly stop at -25. Which isn't great if you want just a little bit more on the less than zero side and the font will allow it.

And here's a random bit of info for developers. The attributed string value for setting this value is NSKernAttributeName, which the documentation describes as "points by which to modify default kerning", but what it doesn't mention is that this seems to be a percentage of the font size.

That is all. Please continue on with your Saturday.