Mixxx is the only Linux-native DJ software that I know of, but it's still amazing. If it's missing featutes compared with Serato or Recordbox I'm not good enough to miss them yet, and the features it doea have are damn impressive.
Likewise, Inkscape and Gimp are both great. I know that Gimp takes a lot of heat for not being as "good" as Photoshop, but it's just different. The few times I've tried Photoshop were as painful to me as Gimp seems to be for others. And since I don't need the CMYK functionality that Gimp is missing, I'm happy with Gimp.
LaTeX has a steep learning curve, but using anything else for documents is like stone knives and bearskins in comparison.