Oft is an old-fashioned, poetic form of often. It appears as a prefix in some fixed expressions in literature and poetry.
The oft-repeated story sounded familiar.
An oft-told tale of heroes.
Often can mean about or around a time or number. It shows estimation and is not exact. This use is less direct but common in speech.
We often meet around seven o’clock.
He often takes five minutes to finish.
Often is used to talk about how common a feeling or condition is. It shows regular presence of states or emotions.
This problem often causes worry.
He is often tired after work.
Often can be used to point out repeated faults or habits in a soft way. It often appears in speaking to suggest something gently.
You often forget your keys, you know.
He often talks too fast for me.
