Yeah, don't sign up for zwift. Nobody goes there any more, it's too crowded.
I find it keeps me engaged a lot better. I was using trainer road and it was going so well that I managed to overtrain. Ever since then I have had trouble making gains on TR. So it's hard to make myself do the workouts. With zwift, I can go as fast or slow as I want. Although if it weren't for group rides with people I know, I probably would just sign up for Rouvy.
If you just want to do workouts, I am pretty sure you can use Golden Cheetah.