"Everything" is an administrative tool that locates files and folders by filename instantly for Windows. Unlike Windows search "Everything" initially displays every file and folder on local or removable NTFS volumes on your computer (hence the name...
DocFetcher is a portable German/English open source desktop search application. It allows you search the contents of documents on your computer. - You can think of it as Google for your local document repository.
This package is a personal full text search package which is based on a very strong backend (Xapian), for which it provides an easy to use and feature-rich interface.
Agent Ransack is a tool for finding files and information on your hard drive fast and efficiently. When searching the contents of files Agent Ransack also displays the text found. Users can then quickly browse the results without having to separately open each file!
Spotlight is the system-wide desktop search feature built into Apple's OS X operating system since version 10.4 (Tiger). Backed by an index of all items and files on the system, it's designed to allow the user to quickly locate a wide variety of items on the computer...
RecentX is an innovative launcher that gives you instant access to your files, folders, programs, websites & clipboard history. It automatically remembers your favorite & recent items so that you can launch them even faster.
GNOME Do allows you to quickly search for many items present on your desktop or the web, and perform useful actions on those items.
The program seems to be no longer updated. Last version, 0.95.3, released on November 2014, can be still downloaded from Launchpad.