Every cryptocurrency before Myriadcoin has allowed only 1 algorithm to mine the blockchain.
It's actually not the first coin to do this. There is a pretty old/dead coin called RUC (russian bitcoin), created in 2011, which is both SHA256 & SCRYPT.
It is not open source AFAIK.
https://bitcointalk.org/index.php?topic=48582.0;allGood point. I'll change the wording. I wondering why RUC didn't catch on more? Not being open source will kill things harshly it appears.