Pool Solutions/Pool Forum hasn't died, though without new members they haven't been as active recently.
BleachCalc is the same as always. I assume you are actually talking about my Pool Calculator, see the link in my signature, which includes a CSI calculation.
The CSI (Calcite Saturation Index) is very much like the LSI (Langelier Saturation Index) but a bit more accurate. LSI includes several approximations designed to make it practical to calculate with a pencil and paper. CSI is designed to be calculated by a computer, so it doesn't need to use as many approximations.
Both of these indexes are designed to give you a sense of which situations are likely to result in pitting of plaster surfaces or calcium scaling. CSI values below -0.6 suggest a possibility of pitting of plaster surfaces. CSI values above 0.6 suggest a possibility of calcium scaling.