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https://www.rgtcycling.com/ no idea if more 'fun' but is currently free.
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Quick summary of all the options and free trials here: https://bikerumor.com/2020/03/15/every-indoor-training-platform-compared-zwift-vs-kinomap-vs-rouvy-vs-sufferfest-vs-veloton-vs-bkool-vs-cvrcade-and-more/
Only tried RGT so far, graphics seem beyond my laptop which does Zwift fine.
Basic RGT is always free but you can currently get Premium features for free as well, not activated that yet.
i have a zwift subscription, what is more 'fun' and free out there?
fuck training and stuff like trainerroad/sufferfest