In the low-level front, I've used Assembly, C, C++, and willing to learn Rust (or D?).

In the too-high-level front, I've used PHP, Python, JavaScript, Ruby, but not willing to use them again if I can avoid it.

These days all my new code is written in F# (or TypeScript if I need to use some JavaScript library), although I still need to touch a lot of C# code.

When I was freelancing, I was willing to learn Elm in case I needed to do some web+frontend development and they didn't let me write TypeScript in strict mode (plus tslint).

Or Ceylon/Kotlin/Frege (along with ParparVM if iOS is needed) or Swift, in case I needed to implement mobile apps and they didn't let me use Xamarin.Forms+F#.

In regards to databases, I'm an old-school guy who thinks normalized data usually beats any NoSQL/NewSQL solution, except for rare BigData indexing/denormalization scenarios.

If you're interested in F#/Rust/crypto remote job opportunities, ping me.