symja_android_library's rule dump in their repo and that seems attractive.
MathematicaSyntaxTestSuitewould also help loads.
However to select between antiderivatives which are both valid, Rubi assumes the integrand' s variables are positive. For example,
Int[1/Sqrt[a + b x + c x^2], x] returns
Int[1/Sqrt[a + b x - c x^2], x] returns
Note that both results are mathematically valid no matter what nonzero value is substituted for c and both results are free of the imaginary unit if a positive value is substituted for c.