Fedora Labs is a selection of curated bundles of purpose-driven software and content as curated and maintained by members of the Fedora Community. These may be installed as standalone full versions of Fedora or as add-ons to existing Fedora installations.
The Fedora Alternative Downloads are either special-purpose - for testing, for specific architectures - or are more standard versions of Fedora in alternative formats such as network installer format or formatted for BitTorrent download.