tmux chain keyboard shortcuts, or equivalent for screen's `bind -c` + `command -c`

After understanding better what you are trying to do, I think a short bash script is the best way to go (sorry, I don't think a tmux-only solution similar to screen command classes exists):

In .tmux.conf:

bind-key x command-prompt -p "launch what?" " "run-shell \"tmux-launcher %%\""

tmux-launcher should be an executable shell script somewhere in your path:

#!/bin/bash
case $1 in 
  o) tmux new-window -n imap -t 10 offlineimap.sh -o ;;
  m) tmux new-window -n mod ncmpcpp ;;
  w) tmux new-window -n vw vimwiki ;;
esac

One drawback is that you must type return after the letter that selects the window to create.

I was recently informed of the switch-client approach to this

to bind join-pane to prefix + t*

tmux bind-key t switch-client -Ttable1
tmux bind-key -Ttable1 '*' join-pane