You are totally right! There is also Curecoin. I am not sure about the Foldingcoin payout scheme, but the big difference between the Curecoin and Gridcoin payout schemes is probably what makes many users think they are hardly making anything at all at Gridcoin relative to the other coins:

Curecoin pays out users daily based on their contribution to the total protein folding compute for the day. You will immediately be paid out at your maximum rate.

Gridcoin pays out based on your Recent Average Credit (RAC), which translates into magnitude (mag). These climb over the course of weeks, and peak after about a month.