Hi! As this is my 9th time around, I thought I'd share the tools I found most useful over the years.

Engine: Stencyl (makes coding quick and easy)
Timelapse: Chronolapse
Audio: https://freesound.org/, http://opengameart.org/ (if you jam) + Audacity
Graphics: Aseprite (for pixelart) or Krita (for drawing) + GIMP (for Layer export & sprite sheet plugins)
EDIT: Aseprite is only free on Linux, but well worth buying.

All those tools are free to use & cross-platform (I dev on Linux Mint) :)