I’m happy Andreas mentioned statsim.net.
I can’t be the only one having a hard time reading things on atc-bookings.vatsim.net.
Statsim has got a really fast search function. When you click on “Tabels” at the top, you can search for any station you want. This is very useful as I search for “CTR” and “APP” bookings as they give me much more ATC covered time than just GND or Tower and I plan my flights according to these schedulings.
Would be a nice statsim feature to show every major airport covered by a Center controller.
I’m sure most people won’t know which airports are covered by EDMM_O_CTR or ENOR_S_CTR without having to do some research…
I’d like to research this data for statsim and invest time in collecting needed data for this feature, but the admin of statsim is only reachable via discord, which I can’t use since I don’t want to give them my phone number 
If anyone knows who is “felix21” on the VATSIM forums, please DM me.
I think it’s a pity that scheduling ATC sessions is not a thing in North America 
Once the PMDG 777 is released, I’d love to do North Atlantic flights when I can expect ATC to be online in the US or CA.
Only BOS_CTR and NY_CTR seem to get scheduled from time to time and therefore KBOS and New York Airports would be the only destinations in NA I could plan flights to, which is really sad
VATSIM could do more advertisement and raise more awareness for the ATC scheduling system as I’m sure also ATC would benefit from it by getting more Pilots to fly to their covered airports.