Synapse is a semantic launcher written in Vala that you can use to start applications as well as find and access relevant documents and files by making use of the Zeitgeist engine.
https://launchpad.net/synapse-project
Tarball: https://launchpad.net/synapse-project/0.3/0.2.99.2/+download/synapse-0.2.99.2.tar.xz
Open Source: Yes