qtractor has nothing to do with agriculture - Qt is the name of the toolkit Rui has used to create his DAW that you can use to create your 'tracs' - hence qtractor!
I'm not going to go over qtractors many features as they're all listed on its homepage. You just need to know that its a reasonably mature, GPL licensed MIDI and audio sequencer for Linux and you really should try it soon if you haven't done so already because its an absolute joy to use!
When it comes to Linux DAWs, for a number of years now qtractor has been the only serious alternative to Ardour. However, qtractor is primarily a MIDI sequencer that also handles audio where as Ardour, as of August 2012, is still yet to make a stable release that includes MIDI sequencing support.
It is important to note that qtractor has a different target market to Ardour. Ardour is aimed directly at high-end, pro-audio users who may otherwise be using non-free solutions like Pro Tools whereas qtractor is aimed more at hobbyist and bedroom/garage studios - well at the moment anyway. Ardour has long been available for OS X as well as Linux but qtractor is proudly Linux only and as a result is one of the very best Linux only apps, not just in audio, available.
qtractor is currently at 0.5.5 which I'd say is quite modest considering what it is already capable of. If Rui continues developing qtractor at the pace he has been over the last several years then when 1.0.0 does get released I have no doubts it will give some of the big name DAWS a good run for their money and will be incomparably better than whatever they released as a 1.0 in most cases as qtractor is obviously very well coded. Outside of running dodgy plugins - I'm not sure I've ever seen qtractor crash and its binary comes in at less than 1MB which explains why it runs sooo fast even on older hardware.
qtractor has often been the first app to adopt new Linux audio technologies such as LV2 with its many updates and extensions. Whilst I was doing lots of testing for Ardour 3 I would frequently use qtractor as a reference. Whilst Ardour, not only because it has a few full time devs working on it and has also been around almost twice as long as qtractor, offers more high end features for audio work than qtractor currently does, I have found qtractor to be much more stable with notably fewer quirks. Rui is always very responsive and intolerant of bugs in his apps.
It is only in the last year or so that qtractor has finally gained some much requested and long awaited automation support for both audio and MIDI tracks. Whilst this works well enough, its not feature complete right now as you can't copy and paste either segments of or whole automation parts yet. My other most wanted feature before I think qtractor is seriously ready for world domination is the ability to create tempo ramps - when qtractor can do both these I'll be made up! qtractors biggest problem is that it is developed purely as a hobby by Rui and that there is no other major contributor to its development so progress in respect to major new features is slow.
AV Linux 6 has just been released so if nothing I've said has put you off I would highly recommend you download that distro (if you're not running Linux already), get it installed and give qtractor a try - I'm sure you'll be glad you did!
To finish I'd like to thank Rui for this outstanding contribution to (Linux) music and audio software. qtractor is not only one of the very best Linux apps in any category, its one of the best apps wrote for Qt, its a reference for others trying to develop Linux audio software of all sorts and Rui's dedication, good humour and exemplary support for all of his apps is to be highly commended.