What is X11 algorithm and How to Mine X11 Coins
X11 algorithm was developed by Dash (formerly Darkcoin) developers and its called a Proof-of-Work (POW). The algo was based on multiple rounds of different hashes (blake, bmw, groestl, jh, keccak, skein, luffa, cubehash, shavite, simd, echo) by making it one of the safest crypto currency in existence.
List of X11 Supported Coins -
How to Mine X11 using CPU/GPU/ASIC Mining
When Darkcoin aka Dash was initially launched with X11 algo, it was only mineable through CPU mining softwares. Slowly the network hashrate has gone upwards and it was widely speculated that someone would have created GPU Miner and to be fair for the individual miners a bounty was announced to create GPU miner that could be available for public. Though GPU has dominated X11 mining, if you have good enough RAM, you can try your hand at mining X11 coins.
The advantages of X11 mining are security, speed in generating hashes for both CPU and GPU at the same time keeping the GPU's 30% cooler for better longetivity of your graphic cards without getting them overheated. Also, due to it's power efficiency reduces your monthly electricity bills to an extent. Comparatively bit more complicated than bitcoins SHA256 algo, makes prevents ASIC mining in near future making it possible to mine with CPU/GPU effectively.
X11 CPU/GPU Mining Software
CPU Miner for X11 and other algorigthms - https://github.com/tpruvot/cpuminer-multi/releases
GPU Minig Software for X11 -
Sgminer 5.0 thread on bitcointalk.org for support, sources and and latest Windows builds: https://bitcointalk.org/index.php?topic=632503.0
CCminer with X11 support: https://github.com/tpruvot/ccminer/releases
Evan Duffield, the creator of Darkcoin and X11 chained-hash, has wrote on several occasions that X11 was integrated into Darkcoin not with the intention to prevent ASIC manufacturers from creating ASICs for X11 in the future, but rather to provide a similar migratory path that Bitcoin had (CPUs, GPUs, ASICs).