General Synonyms:
* Option
* Choice
* Substitute
* Replacement
* Other
* Different
* Another
* Variant
More Specific Synonyms:
* Contrasting (for opposing alternatives)
* Unconventional (for unconventional alternatives)
* Novel (for new alternatives)
* Auxiliary (for supporting alternatives)
* Secondary (for less important alternatives)
Formal Synonyms:
* Alternate
* Variant
The best synonym to use will depend on the specific context of your sentence. Consider what you want to emphasize about the alternative, and choose the word that best conveys your meaning.