The HD Method is a novel 2x2 method and has its own SpeedSolving Wiki and a SpeedSolving Thread by Neuro.
This google document by Neuro fully explains standard HD.
Sue Doenim also created a SpeedSolving thread comparing HD-G and EG.
Proposed by Van Higgs (Thermex) and Joel Demars (Sue Doenim) (-> Higgs-Demars), helped by Max Garza (Neuro) and Johnathan Lewis (Shiv3r).

General structure

HD (Higgs-Demars)

1. V: solve 3/4 of the D-layer, not considering permutation (intuitive, ~1.5 moves)
2. LOLS (Lewis Orientation Last Slot): orient the last five corners (23 algorithms (or 16 if 2x2 OLL is known), 5.5 moves)
3. NLL (Neuro Last Layer): permute all the corners (36 algorithms, 8.13 moves)
   => 59 algorithms, 15-16 moves

HD-G (HD-Guimond)

1. V+CO: orient all corners while solving an unpermuted V by intuitively changing the last move(s) of the algorithm (15 algorithms, 3.90 moves)
2. NLL (Neuro Last Layer): permute all the corners (36 algorithms, 8.13 moves)
   => 51 algorithms, 13.53 moves

Algorithms

The official algorithm sheet, WoowyBaby’s algorithms, spongybaaaaaaasdbasd’s HD document (includes HD-G), their older document, algorithms for Guimond Orientation and my HD-G document.
Very good algorithms for PBL (which is a subset of NLL) can also be found on Will Callan’s 2x2 algorithm spreadsheet.