For emphasis:
* Truly: This is a formal and more emphatic synonym for "really".
* Indeed: Similar to "truly", "indeed" conveys a strong sense of affirmation.
* Actually: This emphasizes that something is true, even if it might seem surprising.
* Definitely: This conveys certainty and is often used to agree with something.
* Absolutely: This emphasizes agreement and suggests a strong conviction.
For expressing surprise or disbelief:
* Seriously: This is a more informal way of saying "really" and often expresses surprise.
* Honestly: This implies that you are being sincere and truthful.
* For real: This is a slang term that means "seriously" or "really".
For softening a statement:
* Quite: This suggests that something is true to a considerable degree.
* Pretty: This is a more informal way of saying "quite".
* Rather: This suggests that something is true to a certain extent, but not necessarily to a large degree.
For other contexts:
* Very: This can be used to emphasize a quality or degree.
* Extremely: This suggests a very high degree of something.
* Totally: This is a very informal way of saying "completely" or "entirely".
Ultimately, the best word to replace "really" depends on the specific situation and the desired meaning. Consider the context, tone, and formality of your writing when making your choice.