Tracktion T7 the latest upgrade, like T6 is also free - hard to argue with that as a proposition. Tracktion have long been an advocate of the single window approach to a DAW, its a simpler to use interface and makes it an ideal starting point for new DAW users. Added to that is the multi-platform support, Windows, OS X and Linux.
New in T7
Clip Layer Effects - each clip (as well as at track level) can have its own effects and plug-in processing
Visual plug-in browser,
Multi-browser for auditioning and placing multiple audio files
Powerful modular racks for creating custom, complex signal processing chains,
Automation patterns, such as LFO and envelope shapes which can be tempo synced.
Tracktion T7 is available for free download now, with discounted upgrade paths to the full WAVEFORM daw.