Learn Swedish: Kanske är allt bra nu. - Maybe everything is fine now.

This is because of the V2 (verb-second) rule in Swedish. Since the sentence starts with the adverb kanske (maybe), the verb är must take the second position. The subject allt gets pushed right after it.

Why does this sentence use allt instead of alla?

Allt is the neuter form of the word for 'all', and when it stands alone like this, it means 'everything'. If you used alla (the plural form), it would change the meaning to 'Maybe everyone is fine now.'

Since allt acts as a neuter word, why doesn't the adjective bra get an extra '-t' at the end?

Normally, adjectives matching a neuter word or pronoun add a '-t' at the end. However, bra is a special adjective that never changes form. It stays exactly the same whether it describes an en word, an ett word, or a plural word!