Since you are saying they are still active and constantly developing their project, then maybe you might be able to make some profit. Do they have an active community too? If they have, then high chance you will make some profit. But what is weird is that it has been almost 3 years and they still aren't listed on any exchange. And you can only exchange on their platform for now, but has no volume. This isn't a good sign. Maybe keep holding it and forget about it. I don't see any other option since you can't even exchange it.