Formal:
* Probablement: This is the most common and neutral way to say "probably."
* Vraisemblablement: This is a bit more formal and implies a higher degree of certainty.
Informal:
* Sûrement: This translates to "surely" but can also be used to mean "probably."
* Peut-être: This literally means "maybe" but is often used to express a hesitant "probably."
* Je pense que oui: This means "I think so," and implies a high level of certainty.
Other options:
* Il y a des chances que...: This means "There is a chance that..."
* Il est possible que...: This means "It is possible that..."
Here are some examples:
* Probablement, il va pleuvoir demain. (Probably, it will rain tomorrow.)
* Vraisemblablement, il a déjà quitté le pays. (He has probably already left the country.)
* Sûrement, elle est déjà arrivée. (She has probably already arrived.)
* Peut-être, il va venir. (Maybe, he will come.)
* Je pense que oui, elle va accepter. (I think so, she will accept.)
* Il y a des chances qu'elle soit malade. (There is a chance that she is sick.)
* Il est possible qu'il ait oublié. (It is possible that he forgot.)
The best way to choose the right word depends on the specific situation and the speaker's level of certainty.