You can visit http://pkgs.slitaz.org then select "file", type in filename, select version and search in which packages this filename pattern exists.
I don't know, maybe it 'irssi'?

It doesn't seem to be availaible at the moment. File a bug/feature request over at http://labs.slitaz.org for it to be packaged. Hopefully someone will pick it up!

Looks like it should be part of the "util-linux-ng" package which is already installed, but write and wall seem to have been left out. I just downloaded the source code and I'll try to compile it. I'll let you guys know if I get anywhere.

I haven't compiled the program, but I wrote my own script to replace wall (At least for what I need to get done).

It's pretty short, only one line.

[code]
#!/bin/sh

for i in /dev/tty*;do echo "$@" > $i ;done

[/code]

I created a file "/usr/bin/wall" and put that script in it.
Made it executable (chmod +x /usr/bin/wall).
Now I just use it like so:
$wall This is my message

It only works for root since, by default, normal users can't write to /dev/tty*
But, it got the job done for what I need to do right now anyway.
I'll still look into compiling write and wall if I have time.