Synapse is a semantic launcher written in Vala that allows the user to easily launch applications as well as search for documents through searching Zeitgeist.
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Pro Includes a Zeal plugin
Includes a Zeal plugin to make searching faster.
Pro Can run commands just as a terminal would
Users can run commands such as
sudo apt-get update from within Synapse, making for a convenient way to open or run items/commands.
Pro Zeitgeist powered
Synapse searches the Zeitgeist log, which tends to be a pretty quick way to do searches over other app launchers.
Con Unable to search whole system
Due to Zeitgeist being used the search is not as robust as if it were using Tracker. Of course using Tracker has its own downside like battery drain, so currently there is no "best" solution.