I use Ride with GPS for routing my rides. In my opinion it is the best software out there particularly for audax (randonneur) and touring.
At the end of a ride my Wahoo ELEMNT syncs with RWGPS and shows a plethora of metrics. One of these is ‘average watts’. As I don’t ride with a power meter and I have only entered my FTP and weight into my profile: How do they calculate my watts? I assume as I ride with a HRM, this may contribute.