OS X: Shortcat[1], Karabiner[2], Moom[3] (or similar), and the Shift+Command+/ shortcut to access the help menu to search app menu items.

Other *nix: dmenu[4], xcape[5]

[1] http://shortcatapp.com/

[2] http://pqrs.org/osx/karabiner/

[3] http://manytricks.com/moom/

[4] http://tools.suckless.org/dmenu/

[5] http://github.com/alols/xcape