You can develop C-41 films in B&W chemicals, even the colour films. Of course they will not develop as colour images, but as B&W. Almost anything will work, but some are better than others. Somewhere above are some Ektar 100 that I did by error in TMax developer. (
Here)
Using 1:100 Rodinal for an hour's semistand (3 inversions at start, and three at 30 minutes) gives an almost grain-free result with XP2 exposed at 200. Plus it's much cheaper than using my C-41 chemicals! I've also done XP2 in Diafine, but it is a little more grainy than the Rodinal. Easily dealt with with the Luminance noise slider in LR if it offends.
Frankly, the reason I do it is to reduce grain—and I know many will reply with all the gory details of their undying love for nice big coarse grain. Photographically, I grew up with cheap equipment with small aperture lenses, requiring fast films such as HP3. So my pictures were generally underexposed and very grainy. The desire to avoid that has stayed with me.
Chris