If you are an employee, this is for you!
There are 2 CPF schemes for you to voluntarily top up money to your CPF account.
They are the 'Retirement Sum Top Up Scheme' and the 'Voluntary Contribution Scheme'.
So what's the difference?
Because there was limited information on the 2 schemes online, we emailed CPF Board to clarify the difference between them.
The difference was not very obviously shown on the CPF website.
As such, we have dedicated this post for it.

TopicRetirement Sum Top Up SchemeVoluntary Contribution Scheme$ Goes To   Special Account (age less than 55)      Retirement Account (age 55 and above)      Ordinary, Special & Medisave Account*   Uses   Retirement only. 
   Funds cannot be used for investments etc      Funds can be used for other CPF schemes   Tax   Contributions are tax-deductible      #Non-tax deductible except if all contributions go into Medisave Account   Interest   SA 4%      OA 2.5%, SA & MA 4%   Contribution ...