This is a ribbon Microphone made by Oktava. They haven't made new versions of this microphone for over thirty years. Therefore, these are really rare and extremely valuable. I was lucky enough to work on a few sessions with an engineer who owns one, and it sure did impress me.
It's really fragile, and old nowadays, so you must make sure to not use it outside the home or studio. Basically no live use. It's a ribbon mic but unlike a lot of more popular ribbon mics it does not have a figure 8 pickup pattern. It's unidirectional, or one-direction. Be careful (extremely careful) not to use this microphone with phantom power, because that will destroy it.
I really like the sound of this microphone quite a bit. Like most ribbon mics, it's got a very warm, smooth sound that recalls the old styles of music such as big band and others. It can work great in a variety of contexts though. This one in particular has a very old, distinct flavor to it. It's definitely not the best mic for brighter, more modern sounds, but it does have a variety of uses. For vintage-sounding vocals, or warm strings, it works wonders. It works great on horns as well. I can use it on guitar cabinets when I'm using a really bright sound that I can't capture with a different kind of mic (which happens sometimes). I like it on piano too, but only for the aforementioned vintage sound. For modern, bright clear piano sounds that are more realistic, it wouldn't work as well. That's fine though, as that's what condensers are for!
I don't know where you'd find this mic, which made me wonder if I should review it. But it was such a good piece of gear that I figured it had to be done. I'll certainly see if I can get more of Oktava's ribbon mics as this one really made me a believer.