Reasonable Scala Compiler
This truly means we still lack a programming language with:    1. reasonable support of object oriented programming.
    2. reasonable support of functional programming.
    3. solid concurrency features.
    4. runs comparable to native code.
    5. simple to learn.

Even though it is not difficult to create such a language but we see a new language poping out every now and then and none of them try to solve these issues.