そうだ I heard that, It is said that

らしい ① and そうだ both convey information heard from another source, but with different nuances. らしい ① suggests hearsay with some degree of certainty, implying the speaker believes it to be true, e.g. 'Apparently it's (A)'. In contrast, そうだ is more neutral, simply meaning 'I heard (A).' or 'They say (A).'. They also connect differently to nouns and な-Adjectives, e.g. 大変らしい vs. 大変だそうだ (both meaning 'It seems difficult.').

Both ときいた and そうだ express hearsay, but with different nuances. ときいた means 'I heard (A).' and conveys information directly heard by the speaker, e.g., 高いときいた ('I heard it was expensive.'). In contrast, そうだ reports hearsay in a more abstract fashion, similar to 'They say (A).' in English.

といわれている and そうだ both report something heard, but differ in nuance. といわれている is more general and formal, e.g. 'It is said that (A)'. On the other hand, そうだ often implies someone specific said it and is more casual, e.g., 雨が降るそうだ ('I heard it's going to rain.').

Both forms express observations similar to 'seems' or 'appears', but differ in nuance. そうだ is based on sensory clues, e.g. 雨が降りそうだ ('It looks like it'll rain.', because the sky is dark and the air is damp). ようだ is based on more concrete information or experience, e.g. 雨が降るようだ ('It seems it'll rain.' because people are carrying umbrellas, or the weather report said so).