"It's not a zero-sum game" - In a world of finite resources, land/oil/water it is in fact a zero sum game. Either I own the land or you own the land. We aren't making any more land.
q isn't open source but it is widely used by most major banks to analyse their time series data and there are very well paying and interesting jobs available.
Long time HN lurker...I've worked with kdb+ / k the last few years, it's in every major bank and is great for storing and querying market data. If you're looking for a nice GUI I use qStudio, it helps make it a little more friendly.
Then there are great tutorials on the code k website. It's a beautiful language full of unique original ideas.