We've all seen the computers of Felicity Smoak and every other similar character with similar environment in Hollywood shows. Is everything going on on the computer screen real software applications or just animation?
I suspect the cheapest option has been used, namely mock-ups using PowerPoint.
All the actor has to do is click the mouse or poke the screen and the next slide will come up, sometimes with a transition effect, sometimes with animations inside frames.
My old company used to do this a lot in demonstrating software - it would all be mocked up screens and the sales people would simply move the mouse to the right place and click - customers were fooled into thinking it was real software being used.
I guess that computer screens can also be added digitally in post-production. This provides a was of obviating annoying physical issues like reflected studio lighting - or maybe there's just an automagical anti reflective coating on computer screens for use in film/TV studios.
It has a task bar and all the 'cool things' seem to be windowed applications.
All the things she is doing are likely effects based. And none of the windowed applications i've seen seem like real identifiable things.
The actual OS might also just be effects. It could be custom theme for KDE (that's what it looks the most like to me).
But unless someone working for show or someone who has noticed something recognizable that I haven't,...
I think "Custom skinned modern OS" is best answer at this time.
In season 5, I caught a glimpse of what looked like a spreadsheet on screen when Felicity was doing her thing. It stuck out because the current plot didn't support a spreadsheet being the mysterious hacker juice. I briefly looked scanned through the episodes but couldn't find the clip again. It was especially fast; I had to pause and rewind several times to catch it on screen to study it.
Long story short, it looked like Excel 2016 or Office 365's toolbar, and the window looked like a Windows 10 window. Given the dark color scheme, it's possible that it's a skinned Windows 10. At least, that shot in that episode was.
If I can figure out what episode it was, I'll add in more details and a screenshot. I want to say it's between episode 10-ish and 17.