I just noticed that there are free software to use old Sega games on Windows such as fusion364 (I think it is a free software because it is said at this link, please correct me if it is not).
Now the question is: what about the games themselves? One can easily find some zipped folders or iso files by searching online for old Sega games such as Sonic etc. But is it legal to just download those games without paying any fee and open them with these software on computer and play, or these games are still commercial and one should pay to buy them to play?