sorry there is no one-size fits all solution. The *closest* is Javascript and client-side development isn't that painfull these days but its still Javscript and WILL bite you on the ass.
So I'd say it boils down to either Python or Ruby + Javascript and if I'm honest, I'd say Python has the edge in terms of general applicability. I *personally* prefer the Ruby language, but that's not what you're asking. Breaking it down:
Server side, backend = Python+Django OR Ruby+Rails if you want to get stuff done and stay sane. Ruby should be considered Linux only server side, but then server-side should be considered *nix only. Node works but...its javascript.
Server side Scripting = Python/Ruby are both sensible choices. I prefer Ruby as a language but Python is a safer choice given the library support and performance. The exception is server/cloud management for which Ruby still has an edge (debatable, I know).
GUI/Desktop Clients, Python + QT. Great combination. Its possible to use QT with Ruby, it just doesnt feel right though.
OSX/IoS/Android - Ruby/Rubymotion. Really, really nice if you're developing for the Apple side. Android support is early days.
Browser - Javascript + Framework + UI components of choice. Learn javascript, one framework and one set of UI components and you're set. Well, until you need something a bit different....but its Javascript.
BTW I said I'm a Ruby guy but I've 10 years of Python experience. If the project is suitable though I'm more productive with Ruby (with 18 months experience) but it really is a case of the right tool for the right job.