should be packaged now:
http://hg.slitaz.org/wok/rev/cd8b7d34a9a8
try tazpkg recharge and tazpkg get-install at

@ernia: Thanks. It's not in the packages yet:
"Unable to find: at in the mirrored packages list."
"Unable to find: get-at in the mirrored packages list."
At least I know it's going to be in Slitaz - I've come to rely on 'at' to get things done :-)
I'll try again later.

did you

tazpkg recharge

? i already have at

root@cooking:~# tazpkg get-install at

Connecting to mirror.slitaz.org (94.23.60.116:80)
at-3.1.12.tazpkg     100% |*******************************| 24064  00:00:00 ETA

Installation of : at-3.1.12
================================================================================
Copying at-3.1.12...                                                 [ OK ]
Extracting at-3.1.12...                                              [ OK ]
Extracting the pseudo fs... (lzma)                                   [ OK ]
Installing at...                                                     [ OK ]
Removing all tmp files...                                            [ OK ]
================================================================================
at (3.1.12) is installed.

Yes I did already recharge - three times - and it says there are no new packages. But there is something odd going on ... the gui package manager keeps telling me there are 6 packages to update, and after I try updating the package manager says 0 packages to update... until I do a recharge and then it says 6 to update again - the same packages each time.

I also downloaded the 'at' package manually and tried to do install it with 'tazpkg install --force' but tazpkg reports it can't find the package.

So maybe there's something wrong with my package manager.

if i'm not wrong tazpkg has been upgraded, try tazpkg get-install tazpkg (eventually --forced) from a terminal and retry.
i don't use the gui package manager

Thanks for your help, but it didn't make any difference. My tazpkg was already on version 3.4, but I reinstalled it anyway. I'm still getting the same problem - "0 new packages" and "Unable to find at". I'm starting to think my tazpkg installation is broken somehow. Is it possible my tazpkg is going to a mirror that hasn't been updated yet?

sorry, i thought you were on cooking, the new package is for cooking, you will never see it in stable repository.
download the package and install it with

tazpkg install at-3.1.12.tazpkg

and check if it works well.
if it does not work well you need to install tazwok and rebuild the package against 3.0 toolchain using the cooking receipt

According to the grub menu I am on cooking... is the tazpkg version for cooking later than 3.4? Regardless, I get the same errors with at-3.1.12.tazpkg.

fabio@cooking:~$ tazpkg search tazpkg

Search result for: tazpkg

Installed packages
================================================================================
tazpkg                  4.1.3             base-system.
================================================================================
1 installed package(s) found for : tazpkg

Available packages name-version
================================================================================
tazpkg-4.1.3
tazpkg-web-1.1
================================================================================
2 available package(s) found for : tazpkg 

is tazpkg pointed to cooking mirrors:

root@cooking:~# cat /var/lib/tazpkg/mirror
http://mirror.slitaz.org/packages/cooking/
http://download.tuxfamily.org/slitaz/packages/cooking/
http://mirror.switch.ch/ftp/mirror/slitaz/packages/cooking/
ftp://mirror.switch.ch/mirror/slitaz/packages/cooking/
http://www.gtlib.gatech.edu/pub/slitaz/packages/cooking/
ftp://ftp.gtlib.gatech.edu/pub/slitaz/packages/cooking/
http://mirror.lupaworld.com/slitaz/packages/cooking/
http://slitaz.c3sl.ufpr.br/packages/cooking/
ftp://slitaz.c3sl.ufpr.br/slitaz/packages/cooking/
http://slitaz.mirror.garr.it/mirrors/slitaz/packages/cooking/
ftp://ftp.pina.si/slitaz/packages/cooking/
http://distro.ibiblio.org/pub/linux/distributions/slitaz/packages/cooking/
http://ftp.vim.org/ftp/os/Linux/distr/slitaz/packages/cooking/

read this http://forum.slitaz.org/index.php/discussion/2187/how-to-upgrade-to-slitaz-cooking/#Item_4
if you have not done a lot of work maybe you could restart from scratch, your system seems to be a little messed up

run tazpkg as root, i did install at in stable without problems

Thanks again. Yes I've been running tazpkg as root. And I agree it seems my Slitaz installation is messed up somehow. I'm new to Slitaz, and I haven't done much with it yet - just installed a few bits and pieces with the gui package manager. The first update I did installed the 'cooking' menu item in grub, but apparently it didn't set it up properly. I think I'll do a complete reinstall and see what happens.