Singapore Swap Offer Rate (SOR) is " the expected forward exchange rate between the US dollar and Singapore dollar." and is simply the rate that one would have to pay if he or she would to borrow in US dollars.
SOR comes in tenure of 1-, 3-, 6- , or 12-month. At the end of the loan tenure, the US$ will be converted into Sing$ to be repaid. However, as it is linked to currency movements, it is more volatile than SIBOR.
Like SIBOR, SOR is set by the Association of Banks in Singapore, and is also publicly available.
Some residential property loans in Singapore are pegged to SOR, but SOR-pegged mortgages are not as popular as SIBOR-linked mortgages or Fixed Deposit Rates linked mortgages due to its volatility.
References
Singapore Swap Offer Rate (SOR) Wikipedia(Text) CC BY-SA