nice software, GTK based mostly

Music player - Deadbeef
Volume "wheel"- volumeicon for alsa
Terminal - ... configured UXterm
Calculator - xcalc or galculator
Windowed file manager - PCmanFM
Double tab file manager - Sunflower
Greate light calendar - Gsimplecal (if program is not running, start it, otherwise stop it)
PDF viewer - Epdfview Evince
View picture and photo - Geeqie
3D graphic and animation - Blender
Image editor - GIMP the best (+uforaw for RAW photos)
Another image editors - rgbpaint, xpaint, ImageMagic 
Vector graphic - Inkscape
Multi display manager - Arandr
Lightweight X11 keyboard switcher - fbxkb or xxkb
Run dialog  - grun / gmrun


Photo panorams - hugin
Photo light and shadows - darktable
Photo hdr - luminance-hdr
Photo RAW - darktable, RAWTherapee (link)