Use arrow up/down to browse history, like a true console.
Press alt-arrow up/down to browse history, but just the function.
Repress Enter to evaluate expression again.
Use ans() to refer to previous results, or ans(x) to retrieve the xth to last result.
When you press an operation like *, assumes ans()
Auto-paren completetion. sin(4 doesn't throw an error, it behaves like sin(4)

Store functions in memory. Create functions at runtime, "myfn = function(a,b){return a+b}"
Use tab to autocomplete a function name.
Use constants PI, E

Documentation, even for functions built into JavaScript. "sin.doc()" (but many functions are still undocumented)

trisolve(s) //solves triangles. Try trisolve('3,4,5'), trisolve('3,3,45o'), trisolve('45o,45o,5')
factorial(n) //works on non-integers, too
permutation(n, r)
combination(n, r)

factorize(n)
gcd(a,b), lcm(a,b), isprime(n)
randint(lo,hi)
chbase(x,base) //Change base
deg2rad(x), rad2deg(x)

Array utilities: sum(an), mean(an), mode(an), vari(an), min(an), max(an)
det(m) //matrix determinant, credit to http://mkaz.com/math/

ans([x]) //previous result
echo(s) //print to console
clr() //clear console
doc() //print list of available functions

Also, methods of the JavaScript Math class are exposed