Cycling Analytics has a 30 day free trial period. I played with it and Wattsboard at the same time; both follow the same format of a free trial before subscription. I personally like the format from Cycling Analytics since it's clean and still provides a good amount of data. Wattsboard also has a clean GUI and display. Both will allow you to upload files without a subscription but what you're paying for is the ability to deep dive into a specific ride and figure out what's happening. What I like with Intervals.icu is being able to dive into a specific ride, since it pulls from Strava, you're able to see your efforts by Strava segment.

There's a lot of good options but if you're looking for free, Intervals.icu, Elevate and Golden Cheetah would be what I'd recommend. I would say that GC is not really user friendly but has a lot of features that I'm sure that I haven't discovered.

I don't know if it was covered but these tools work best with a powermeter and HRM; it's the only way to see what's going on and if you're making progress towards a specific goal or training plan.