glow
cat for Markdown files. It’s practically useless, completely unnessary, and I use it all the time. 
celluloid
A GTK frontend to mpv. I found it after getting fed up with one of Parole’s (Xfce’s default media player) many, many bugs. It’s clean, runs great, and even has a couple of surprisingly helpful settings, like enabling / disabling client-side decorations.
gtk3-nocsd
Speaking of client-side decorations, I don’t like them. They’re a massive eyesore IMO, especially when I’m using a WM that doesn’t show header bars, like bspwm. gtk3-nocsd fixes this by moving menu items down and removing the client-side decorations with a very small number of issues. It’s also actively maintained.
Another program that accomplishes the same purpose in a different fashion is gtk-mushrooms - currently looking for a maintainer, it’s a patched version of GTK.
netsurf
Cool modular browser with a completely unique engine. Lightning fast, but lacks proper Javascript support.
hexyl
Colorful hex viewer.
grex
For those bad at regular expressions.
qalc
Command-line calculator - faster than starting up a Python console, and with much better syntax / functions / division than bc or similar.
timeshift-autosnap
Backs up your system before any upgrades. Regardless of whether you already use Timeshift or not, this is worth checking out.
gotop / ytop
Somewhat of a middle ground between htop and bashtop.
