You can do a large amount of Judo without a gi (for either you or your opponent), but it needs training, like KFW suggested. The Judo that is contained in NGA is typically performed without relying directly on the clothing, except in a couple of cases, where even a sturdy t-shirt would serve.My post was responding to the few previous posts saying Judo is not that good. I am only saying that it's not that bad if compare to TCMA that are striking only.
Wrestling and BJJ are on the TOP of the food chain of fighting arts, you don't talk about them in the same breath with the lower ones that are swimming close to the bottom. If I were 40 years younger, I would learn wrestling or BJJ together with Mauythai, forget TKD or other TMA. Some Judo is good for falling at old age, it is valuable.
You can still do something without the gi in Judo, limited, but you still can. You can still grab the person and do hip throw, or trip them backwards. I forgot all the names already.