LCD-i4

Audeze isine and LCD-i are the main ones. I think goldplanar might have also done a large diaphragm truly open back planar IEM as well, but that's about it. Unfortunately they're all completely broken in terms of tuning, and need heavy EQ work to sound normal. If you're hoping for one that sounds good out of the box, it's not going to happen. Most of what people refer to as "open" or "semi open" are just pretty conventional front and rear ported IEMs. The only difference being that they tend to have the back porting on the outer face rather than the side or inner face.