There are at least 5000 satellite TV&radio channels in Europe alone that have nothing to do with Sky.
BSkyb (the UK end of their operations) rents a number of transponders on the Astra2 satellite, and since the demise of their analogue transmissions on Astra1 that's the ONLY satellite they use. Some of their programming (Sky News) is sent out in various other providers' packages on various other satellites, but aside from that, every frequency on every satellite other than Astra2 is from some other organisation.
The Astra fleet of satellites is owned by a pan-European consortium SES, and they rent out transponders to whoever pays them. Other providers using transponders on Astra2 include Felxtech, TVX, a seemingly endless parade of religious and shopping channels, ITN news, etc etc. Some (but not all of them) pay Sky for an entry in their EPG; some pay for use of Sky's transponder capacity; some pay for the use of the Videoguard encrption system; some are entirely independent.
Also co-located at the same 28.2e orbital slot as Astra2 is the Eurobird satellite, which is used by other European providers too, and some of whose channels can be picked up by a Sky box (though they have nothing to do with Sky).