I want to encourage people to think of sympy not just as a competitor to Mathematica but additionally as an incredibly valuable library that can be used _inside

I want to encourage people to think of sympy not just as a competitor to Mathematica but additionally as an incredibly valuable library that can be used _inside_ of other projects. Sometimes, you just want to compute an antiderivative, or you want user-supplied functions that you can manipulate easily, or you want to do some actual algebra. Think of it less as a Mathematica replacement (like "Linux on the Desktop") and more as a crucial library enabling a lot of fun new creative things (like "embedded linux running on your toaster"). For example, in some of my computational chemistry work we use it to allow users to specify certain functionals, which we can then manipulate symbolically, do expression reduction and elimination on, and prove certain properties about. It's great!