Swift.
It's a wonderful language, it's general purpose, it's cross platform, and it's open source (Apache license). I wish it was a mainstream language outside the of the Apple universe.
What I love the most is it's so flexible. It's a full featured OOP language, a full featured Procedural language, a full featured Functional language, a full featured declarative language, and you can relatively easily make it work with anything else you can think of.
It also has the best concurrency system I've ever seen - and with high performance computing relying so much on parallel computing these days that's a must and often what I miss the most in other languages.
A lot of other languages do some things just as well as Swift, but Swift does everything really well.