Quicksilver
Used by 29 peopleqsapp.com ↗

“I was an obsessive Quicksilver user back in the day, and then I switched to LaunchBar during that dark period when QS wasn't being supported.”
Gabriel Roth Interview, Writer, web developer · via Uses This 
“I want to mention Quicksilver as well, a small but awesome launcher utility.”
Sadayuki Furuhashi Interview, Hacker (MessagePack, Fluentd) · via Uses This 
“I can't use a Mac without QuickSilver.”
Chris Ilias Interview, Chef at Sweet Basil, Colorado · via Uses This 
“I'm not a natural customiser - I use Quicksilver solely as an application launcher - but I really enjoy the emacs cycle of change: months spent oblivious to how enraged I am by some process or behaviour or keystroke, a recognition that the source of pain exists, a bunch of Googling, between one and twenty lines of new config, a sigh of relief.”
Mary Rose Cook Interview, Coder, musician · via Uses This 
“I was a Quicksilver diehard for years, but really, the stability (or lack of it) got to me.”
Tom Armitage Interview, Game designer, technologist (Hide and Seek) · via Uses This 

“If most people are using Quicksilver then I think that pretty much points to a badly designed OS.”
Cal Henderson Interview, Web developer, professional asshat · via Uses This 
“I almost forgot - as it's become so basic that it's nearly invisible - QuickSilver, that I use mostly for opening apps and files.”
Steph Thirion Interview, Game developer (Eliss) · via Uses This