Rydex is now called ProFunds, but the Rydex name is still in common use.
Yes they are Mutual Funds and trade once at the end of the day, but they label themselves 'investor class' mutual funds. $15,000 minimum amount to buy in, and no financial penalty for early withdraw, and they are more transparent about the daily money movement into and out of each one.
From what I understand, they trade more like ETF's than mutual funds.