と言(い)う事(こと)だI heard that, Rumor has it that, It is said that, It means that

Both can report hearsay, but with different tone. とか is casual and vague, often implying uncertainty, similar to 'I heard / They say (A), or something.' ということだ is more formal and declarative, closer to 'The word is (A).' ということだ can also be used to draw conclusions (i.e. 'that means (A)'), which とか cannot.

Both can be used to report hearsay (i.e. 'they say (A)'), but differ in tone and nuance. ということだ is more formal and can carry the nuance of summarizing or confidently reporting what the speaker heard. だって is much more casual and light, and can also be used at the beginning of a sentence with an emphatic 'but I mean (A)' nuance, which is something ということだ cannot do.

とされている and ということだ both report other people's opinions. ということだ has a nuance of direct hearsay: 'They say that (A)'. On the other hand, とされている presents something as generally believed or accepted. It's less about quoting someone and more about shared public perception.

Both convey hearsay, but differ in tone and formality. そうだ is used to directly pass on something you've heard, e.g. 明日は休みだそうだ ('I heard he has tomorrow off.') ということだ is more formal and often sounds more confident or declarative. It can also carry a nuance of explanation or conclusion, e.g. 明日は休みになるということだ ('So that means / They say we'll have tomorrow off.')

Both use こと to summarize information, but with different nuances. ことなの means 'it's that (A)' and is often used to clarify or define something, as in '(A) means (B)' or 'that means (A).' ということだ can also be used in this way, but additionally functions to report hearsay, e.g. 'I hear / They say (A).' ことなの, without the quoting function of という, is not used to report what others have said.

ということ turns phrases into nouns and often clarifies what was said, e.g. 日本に行くということ 'the fact that he's going to Japan'. Adding だ forms ということだ, which is used to report information second-hand, e.g. 来年から海外に住むということだ ('I hear he'll be living abroad from next year.').

ということだ and らしい ① both convey information from another source, but differ in nuance and formality. らしい ① conveys hearsay with a nuance of confidence, e.g. 雨が降るらしい ('Apparently, it's going to rain.'). In contrast, ということだ literally means 'It is said that (A).' or 'The word is that (A).', and sounds more formal and confident than らしい ①.