Often, frequently, oft, oftentimes may be used with little or no distinction to mean again and again in more or less close succession.
But often stresses the number of times a thing occurs, without regard to the interval of recurrence; frequently usually stresses repetition, especially at short intervals.
Oft and oftentimes differ little from often; oft, however, is used chiefly in compound adjectives or occasionally in formal discourse and oftentimes is occasionally preferred for intonational reasons.