Dark Gravity Wave
DGW or Dark Gravity Wave is an open source difficulty-adjusting algorithm for Bitcoin-based cryptocurrencies that was first used in Darkcoin/Dash and has been adopted by other digital currencies.
DGW was authored by Evan Duffield, the developer and creator of X11/Darkcoin/Dash, as a response to a time-warp exploit found in Kimoto's Gravity Well.
In concept, DGW is similar to Kimoto Gravity Well, adjusting the difficulty levels every block (instead of every 2016 blocks like Bitcoin) by using statistical data of the last blocks found. In this way block issuing times can remain consistent, despite high fluctuations in hashpower. However it doesn't suffer from the time-warp exploit.
Version 2.0 of DGW was implemented in Darkcoin/Dash from block 45.000 onwards in order to completely alleviate the time-warp exploit.
Version 3.0 was implemented on May 14 of 2014 to further improve difficulty re-targeting with smoother transitions. It also fixes issues with various architectures that had different levels of floating-point accuracy through the use of integers.