A few I know of
ehx (nano pog, micro pog, pog2, hog2, pitchfork)
Boss (all the ps series if I remember right. They've had a few different names the ps-6 which is he current model is called the harmonist i believe, I think one of the older versions was called a super shifter.
Earthquacker devices (tentacle, pitch bay, I think the organizer also)
Digitech(whammy 1-5, whammy DT, both versions of the bass whammy and the whammy ricochet, mosaic is literally a pedal designed to make a 6 string guitar sound like a 12 string but I've never gotten a chance to try one with bass) )
Tc electronic (SubNup)
T-Rex (quint machine)
Fishman (fission bass powechord)
Line 6 m series (m-5,m-9,m-13)
I've had a few. Whammy IV, the new bass whammy, m-5, nano pog. They all have their ups and downs. (Did I just say that lol) anywho the nano pog is closer to an 8 string type of sound out of all the ones I've owned. Because it has a more realistic attack on that articlficial octave up. The pog 2 probably could get even closer because the detune feature would add a bit of modulation which you do naturally get with an 8 string because the two string side by side don't vibrate perfectly together. The whammys for example the octave up sounded good and it tracks very well but it doesn't sound like an 8 string at all. It works pretty good if you run it into a fuzz pedal though. If you're wanting to do the Royal Blood type of thing the guy from royal blood uses pog2 and the boss ps5 on his board. But I'm pretty sure the pog 2 is his main octave up and he uses the ps-6 more for pitch bending. The pog 2 seems to be king of octave ups. I'm planning on getting the new TC SubNup soon. Seems like a decent compromise for me because while the octave up on the pog is nice the octave down is not very usable IMO. The TC seems to be the best thing for getting decent octave up AND octave down sounds.