Custom Sequence Generator

Does some one have an example of how to create a custom Sequence Generator. Here is a few examples,

  • One customer wants to have the sequence as FB0317-01…02…03 and so on.
  • Then in the same application and same company they want to create and use a new sequence FB170301-01…02…03 and so on
  • Then a new customer wants to create a new sequence in the application OB-01-03-2017… OB-01-03-2018.
  • Here I want to hook the sequence to Entites at runtime.
  • They also want to create new sequence and see all the sequence in on table and be able to modify the sequence if they have to.
    How can I achive this?