With FlixBus, apart for now with the COVID-19, you can buy a cool InterFlix pass for 99 EUR. While hitchhiking is awesome, there are sometimes when traveling by bus has interest too. With the pass you get five vouchers that you can use on any direct route. You can use the nightbuses to sleep and visit another town the next day.
While it's nice to be able to search for itineraries when paying for a normal ticket, it's of no interest to the vagabond user armed with his InterFlix pass. As such, one can look for routes with the interactive map on their website where one can input the town they're in and see all of the possible destinations. Sadly still, some stops are not shown on the map and it has certain limits to how much an user can plan their journey forward (just try it yourself).
What is great though, is that FlixBus offers corporations access to their schedules in the GTFS format. What that means concretely, is that the French Government makes the routes for Europe available under its OpenData policy, and the rest is also visible on TransitFeeds! I'll try to use this data to make a wikified page of the main routes FlixBus seems to have. Though I'll probably never get to it completely, it can still be of interest, along with the link to the data.
My abilities on this are limited, but following GTFS specifications, one would be able to make a real-time map of all the buses routes with names and stops. But you know, it's FlixBus's job :(