The closest analogy that I have found is Ostrich, though that tastes of beef and liver. Venison, aka deer, is much like beef, but with almost no fat, so you have to mix it with a fatty meat to use it as beef, even then there's a richer "beefyness" to the end result.

I wish I had tried an antelope steak, when I had the ability to do so, I suspect that would be closer to beef in taste and fat content upon further research.

Source: over 20 years as a chef.