I make minor use of an open-source software library called Allegro 5 that essentially exists to save C++ developers on overhead code dedicated to drawing to the screen, window creation, playing audio and other simple tasks like that, but the rest of the code is written by me exclusively for Deep! All of the 20k+ lines of code have been written in Visual Studio (VS2010 at the start of the project, and VS2013 as of last year). For making the graphics (sprites, effects, menus etc) I have always used and will continue to always use Photoshop CS3 Extended Edition.
There are various other tools that I use to assist in the game's promotion too. I capture gameplay videos with OBS (which is free and awesome) and I use a program called Gifcam (which is free but you should donate to the awesome developer!) to record high quality animated .gifs right from the game as I'm playing it. Hope this answers your question!
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