The second way, I discovered last week, is Turbo Training. It's a UK based website that allows you to create interval sessions for riding on your trainer. It also lets you use workouts created by other users. The only downside is that you need to be able to see your computer screen from your trainer. I just set my laptop on a hightop chair right in front of my bike. Another thing you may want to watch out for is the screen saver. I forgot to turn my off and it popped up every 5 minutes so I had to reach over and hit the touchpad.
There are a lot of workouts on there and I think the max time is 60 minutes. Some of them are more detailed than others and you can rate the workout after you do it. The better workouts have a suggested cadence, heart rate, gear and/or power (if you have a power meter). To use the sessions you have to create a profile and you can enter a resting heart rate and max heart rate. The website then determines you BPM for each interval of the workout. It works sort of like a Tabata timer as you can see in the picture below. When you click "start" it gives you about 5 seconds to get on the bike and then starts. The big blue timer is the overall time completed. A small green timer will countdown the seconds left in each interval right above the blue timer. The interval you're in will enlarge and you'll hear a beeping sound a few seconds before the next interval is starting. I did the Pyramid workout below.
I'm not quite sure about all the details but, it seems as though you're only allowed to use 3 different workouts a month (as many times as you'd like) and create 1 workout a month. The Premium version is £12 a year.
It worked great for my first time using it and the hour went by fairly quickly vs. just pedaling for an hour.