RGT has a free version, usually just a couple of routes/courses but it's a bit like zwift though more focused on realistic simulation. I believe they have a trial you can sign up for to use all the features of the program.
I've been using fulgaz, it's like rouvy in that it's got video but I've found the videos to be almost all high-quality, and all shot from bicycles. I guess if you don't have a fully working smart trainer you can just watch the videos in "steady" mode and crank out some watts independent of the simulated terrain of whatever app you're using.