And even simpler is the iota combinator which is by itself turing complete. So a single letter plus matching parens is about the simplest language as you can get. But I can't imagine anyone wanting or even being able to program in it.
Assembler is a bad example for simplicity. Perhaps brainfuck fits better in this case.
Simpler aka Python, Ruby, Basic, Pascal, not "lower level".
i don't see those languages as being "simple". quick to program in, yes. but assembler is really pretty transparent, once you get into it. heck, i used to program in machine code (i don't recommend it) without too many problems.
"Simpler" isn't really a good adjective to classify languages. You have to be way more specific on what "simple" means. Are we talking characters needed to implement 'hello world?' Time to first memory access segfault? Number of pages in the specification (which, at this point, I'm not sure whether Python or C++ wins out...)? Lines of code in the compiler / interpreter?