What is Qtractor?
Qtractor is an Audio/MIDI multi-track sequencer application written in C++ with the Qt framework. Target platform is GNU/Linux, where the Jack Audio Connection Kit (JACK) for audio, and the Advanced Linux Sound Architecture (ALSA) for MIDI, are the main infrastructures for Qtractor to evolve as a fairly-featured desktop audio workstation GUI, specially dedicated to the personal home-studio.
Qtractor is free/libre, open-source software, distributed under the terms of the GNU General Public License (GPL) version 2 or later.
Comments and Reviews
Said about Qtractor as an alternative
If you are a Linux user, Qtractor is the best choice for a free and opensource DAW. Nothing is limited. You don't have to upload your work to some random website.
Qtractor is a full fledged DAW for Linux. Unlike FL, it is not available for Windows or Mac. It also lacks the graphic refinement of FL as well as the powerful suite of bundled tools. While it's an alternative, it's not one of the closest.