Theirs Picaxe and Arduino. But any others?

3 small questions actually:

First:

So I've LITERALLY just recently taken an interest in robotics. it seems like a fun, relatively cheap hobby. That being said i've been programming for 7 years. So Im used to C/C++.

SO would Arduino be a better pick for me? I pick up new languages very quickly (i've had to for college). But with Arduino being Based off C........I figure....it might be better? That being said any disadvantages/advantages to using one or the other?

second:

So we have picaxe and arduino. are there any others? or is that just what people mainly use?

third:

I know Arduino is "based" off C (i think). But....like hard coded language deep down to the core what is it? I know it's obviously not a C language. But deep down what exactly is it? Im not really that familiar with EE/Firmware languages. Is it just Assembly? or MIPS code.......i must admit Im a complete newb when it comes to that. I know some Assembly, but I more just wanna understand how the software works as well.

Thanks and sorry for the multiple questions hehe :)