Here you can plot direction fields for simple differential equations of the form y′ = f(x,y).
This page uses javascript witch CSS rotations. This works in most modern browsers. The y′ function should be a javascript expression. It is evaluated in a “with Math” block, so you can use functions such as sin(x) and pow(y,2). Javascript supports the arithmetic operators: +, -, *, and /, and % for the modulus. Here's an overview of the Math object.