- Ulauncher provides instant search results. It also remembers your previous choices and automatically selects the best option for you.
Cerebro is an open source and free electron-based productivity software alternative to Alfred and Spotlight. It is focused on speed and good UI and UX. In most cases you don't even need to open another application, because you can see results right in Cerebro, like google...
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The program seems to be no longer updated.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.
Unleash.so brings all the scattered pieces of data from your cloud and computer right to you. You can search across your workspace, launch web pages and take quick actions from one search bar, such as: RSVP events, start AWS instances and more.
Curiosity is a search and productivity app. It puts all your information at your fingertips so you can focus and get more done.
Launch Box is generally an application launcher. It's very influenced by Quicksilver for Mac OSX. Remember that this is only a first release so don't get your hopes up too much. Launch Box is written for the GNOME 2.10 platform and depends on GTK+ 2.This app doesn't have any features at the moment.Discontinued
This app seems to be totaly discontinuited. The official page on Gnome project points to an inexistant git repo. In Debian archives, last known version is 0.2-1.1:https://archive.debian.net/fr/source/lenny/gnome-launch-boxActivity at FTP link dates back to 2009:http://ftp.gnome.org/pub/GNOME/sources/gnome-launch-box/