[evilduck]

Most (all?) Spotlight replacements depend on the same underlying index and system services that Spotlight provides and uses. High chance Quicksilver is just making 'mdfind' calls like everything else, especially since it doesn't look maintained anymore.

[auxbuss]

LaunchBar doesn't use Spotlight's data. And so, as a result, can't search for data inside files. That said, it provides a Search in Spotlight command – that you can assign a shortcut, if you wish – which returns its results in a new Finder window.