Unlike CryptoNight and Equihash which are specifically designed for Proof of Work blockchains, scrypt was originally designed for another use case. In cryptography, scrypt is a password-based key derivation function KDF. Password based KDF are designed to be computationally intensive and they are efficient at preventing brute force attacks. The algorithm was designed by Colin Percival.
Scrypt offers high level of security and is one of the safest hash functions out there. Also being a memory hard algorithm it improves network security by resisting large scale custom hardware attacks. Because of this scrypt is considered to be perfect for distributed systems. Due to large amounts of memory requirements performing large scale custom hardware attacks on scrypt gets costly.
This hash function is designed in such a way that it requires miners to generate numbers quickly. This then needs to be accessed on a continuous basis before submitting a result. You can read about the importance of ASIC resistance here.
Today Scrypt is being used by a number of proof-of-work cryptocurrencies. But that project failed and it no longer exists. Later coins like Litecoin and Dogecoin started using scrypt. Scrypt was implemented on blockchain networks and it was initially introduced as an attempt to improve upon SHA Its high security is what lead projects like Litecoin to implement scrypt as its hash function.
Meaning there were no custom hardware device on the Litecoin network. Only GPU miners were mining Litecoin. However in the first ASIC for scrypt algorithm appeared. ASICs are superior. There are a lots of ASIC that are capable of mining scrypt coins but only the few advanced ones are actually profitable. According to ASIC miner value only the following miners are profitable at mining scrypt coins currently. Only if you own any of these machines you should think about mining the following list of scrypt cryptocurrencies.
Also note that in terms of overall hashpower scrypt networks have a lower hash rate than SHA networks. Its because of the memory intensiveness. However, what differentiates the Scrypt function, from the SHA function, is that it is also memory intensive. Scrypt is memory intensive because as well as requiring miners to generate numbers rapidly, these generated numbers are stored in the Random Access Memory RAM of the processor, which then needs to be accessed before submitting a result.
In terms of overall hashing power, Scrypt based protocols have a lower hash rate than SHA based protocols. Currently, according to Blockchain. The Scrypt hash function was initially implemented by the Litecoin development team to avoid what are known, Application-Specific Integrated Circuits ASICs , from being able mine on the Litecoin network.
Therefore, miners who use any other device other than an ASIC to mine for a cryptocurrency, are put at a disadvantage. Scrypt-capable ASICs have been developed that allow for efficient mining of any cryptocurrency that use the Scrypt algorithm. Cryptocurrency Litecoin Technology.