General hotkeys:

Ctrl+Tab - switch between File Manager and Music Player.
Ctrl+Shift+Z (global) - capture a screenshot (full screen).
Ctrl+Shift+A (global) - capture a screenshot (active window).
F1 - open Settings.
F3 - search.
ESC - close Image Viewer or clear search boxes.

You can close the program without confirmation with Right Mouse Button or Wheel Click

Music Player (global):

Ctrl+1 = play/pause.
Ctrl+2 = stop playback and free the file.
Ctrl+3 = play previous file.
Ctrl+4 = play next file.
Ctrl+Plus/Minus = change volume.

In Playlist, you can use Right Mouse Button or Wheel Click to quickly open folders in File Manager.

File Manager:

You can click on favorite folders and path folders with different mouse buttons to quickly sort your files:
Left Mouse Button (or F5) = sort files by name/default sorting/refresh folder.
Wheel Click (or Ctrl+Q) = sort files by size.
Right Mouse Button (or Ctrl+W) = sort files by date.
Space - select current file.
Right Mouse Button - select/unselect current file.
Ctrl+A - select all files.

You can search for multiple terms by using the multi-line search box.

Image Viewer:

1 - default image viewer size.
2 - fullscreen mode (info panel).
3 - true fullscreen mode (no info panel).
a - fit image to screen/show unscaled image (toggle)
q, w - show previous/next image (also Mouse Wheel).
Space - select current image (for renaming, deletion, etc).