Right now I'd say the best open-source DAW for Linux is LMMS if you want to do everything just on your laptop, or Ardour if you want to use external instruments.
LMMS has some shockingly versatile built in synths, including a port of ZynAddSubFX, supports LADSPA/LV2 plugins, and supports using Wine to run 32-bit Windows VSTs. I'm unsure of Ardour's VST support, but it at least supports LV2 plugins. Either of those, if you install them through your distro, will likely include Calf Studio Gear, an extensive collection of LV2 effects and a couple synths. As for ones that run natively on Linux, there's synthv1, samplv1, drumkv1, and padthv1, though I've had trouble getting them working myself.
I've found some good stuff on the Linux Audio Wiki but IDK how up to date most of it is.
It's like an avant-garde version of Turn Left, with the concept taken so much further, it reaches the edge of the universe, loops around, and comes all the way back down to Earth.
Did the episode ever explain why everyone runs away in horror, quits their job, and starts avoiding Ruby when they talk to that old woman, including trained UNIT agents? Maybe we weren't meant to know.
I also found it amusing to think about how little happens in the prime timeline. The ultimate result of this entire alternate life is that Ruby has a weird, but brief, supernatural experience, the Doctor narrowly stops himself from breaking a fairy circle, and they both have a normal day in Wales.