HLS


HLS, short for Hessler Last Slot, is a subset of OLS. The HLS substep solves the last F2L pair, if the edge and corner can be paired with one move and can be paired and inserted with three moves by either using (R U R') or the mirror (L' U' L), and it also skips OLL which is the third step used in the widely popular CFOP method. HLS can be used in speedsolving or FMC to decrease move count.
History
Summer Variation, a subgroup within HLS, was published in 2009 by Chester Lian. The naming was based off the name of Winter Variation, a different subgroup within VLS.
The idea of the full HLS subset was created by Rowe Hessler in 2013. He had created a forum post introducing VLS and HLS to the public. He had intended to post the rest of the VLS videos and HLS videos on his and Mats Valk's YouTube channel focusing on OLS, however the channel had stopped posting videos and never finished either of the series of videos. Although the VLS algorithms were completed and published on Rowe's website, not many HLS algorithms have been published anywhere still, and there is likely nobody currently generating any. As of 17 Feb 2018, the only generated algorithms that have gone public for HLS include Summer Variation by Chester Lian in 2006, and 0 by Jabari Nuruddin in 2015.
Learning Approach
There are 8 subsets under HLS. They are named after which edges are misoriented if the last F2L pair's corner and edge pieces are set up in this way (Setup: RU'R'). Note that there are mirrored cases which still fall under their unmirrored subsets. These subsets include SV, UF, UL, UR, UFUR, UFUL, ULUR, and 0 (also known as "all edges"). Each of these subsets include 54 algorithms, if mirrors are counted as separate cases. It is usually recommended to first learn SV and then the rest of HLS in whatever order you choose. Learn the placement of the stickers that are supposed to be placed on the top face, like with OLL.
Pros
 Move count is decreased by about 4 moves compared to normally doing the last F2L pair, then OLL.
 It requires less look ahead, if implemented into solves, compared to doing the last F2L pair and OLL. So, although it only saves 4 moves, decreased look ahead can help reduce your solve times.
 Increased chance of a last layer skip.
Cons
 There are a total of 432 algorithms, including mirrors.
 Because of the first point, this means that if the solver were to learn full HLS, it would likely take at least a year if 1 algorithm was learned per day.