EMBOSS Seqret reads and writes (returns) sequences. It is useful for a variety of tasks, including extracting sequences from databases, displaying sequences, reformatting sequences, producing the reverse complement of a sequence, extracting fragments of a sequence, sequence case conversion or any combination of the above functions.
Simple sequence conversion tool with a diverse set of functions. Site also recommends reading The EMBL-EBI search and sequence analysis tools APIs in 2019 for informed used of available tools.
Very easy to use and self-explanatory