I use Hyperion Prism for framing, focus and guiding. This is an Anglicised relauch of ‘Prism’ which was developed by the French imaging and spectroscopy community. It has slit guiding which I try and use. I used to use PhD2 and I’m sure its fine ( I seem to recall a slit guiding option there too?). Slit guiding needs careful choice of parameters to work properly (it can cause oscillations as it hunts the sidelobes) but when setup properly it seems to work well.
I use PHD2 but I find it can oscillate as Kevin describes. (It has some features useful for slit guiding like a virtual slit graticule and guiding on a specific location but does not have a specific algorithm to deal with a split star image)
I know Astroart has a specific slit guiding algorithm, though I have not tried it.
I think Prism is quite popular among the French spectroscopists. For example Olivier Thizy uses it with scripts to automate his observing
I use Astroart 5 which has a slit guiding facility. You place a cross over the image of the slit in the guide camera window and the software will then keep the star centred on that point. It seems to understand that the image of a star in the slit has two lobes above and below the slit and manages to keep it reasonably stable within the slit, subject of course to the vagaries of seeing. I have used it for years and am very happy with it.