There are a number of exciting projects in the Linux audio that may be of interest here. I'll just name a few, in no particular order, that have tickled my interest.

setBfree - A DSP Tonewheel Organ emulator. https://github.com/pantherb/setBfree

alvdrums.lv2 - a simple Drum Sample Player Plugin https://github.com/x42/avldrums.lv2

The rest of the x42 suite: http://x42-plugins.com/x42/

The zam-plugins suite: http://www.zamaudio.com/?p=976

giada - your hardcore loop machine https://www.giadamusic.com/

Helm - a great sounding (to me) software synthesizer http://tytel.org/helm/

ZynAddSubFX's new GUI http://zynaddsubfx.sourceforge.net/zyn-fusion.html An amazing software synth even without this new GUI.

Guitarix - a guitar/bass amp and effects modler http://guitarix.org/

Bitwig Studio - A proprietary DAW available on Linux https://www.bitwig.com/en/home.html

u-he plugin suit available on Linux http://www.kvraudio.com/forum/viewtopic.php?t=424953

I'm sure there are a few more that I'm forgetting right now.