OLS

OLS, an acronym for Orientation of the Last Slot, is a last slot method used to skip OLL while simultaneously solving the last F2L pair. All OLS cases can be solved using one of the algorithms found in VLS or HLS, although this technically requires two looks because the pair first needs to be set up to a R U R' or R U' R' insert. For example, with the setup R U' R' U R U2 R', the pair can be easily changed to an HLS case by intuitively performing R U2 R' U'. However, setup moves and OLS can be done at the same time if the correct algorithms are used. Unfortunately, this would require up to 17,712 algorithms so it is not put into full use by any human. This method is quite helpful with decreasing times once the solver gets used to using the algorithms. Some notable speedsolvers who use parts of this method from time to time include Feliks Zemdegs, Seung Hyuk Nahm, Mats Valk and Jayden McNeill to name a few.
Contents
OLS subsets
Because of the enormous size of OLS, many subsets of it, which in turn also have their own subsets, exist. The following is an attempt to order all of them.
By F2L case
This is an ordering of substeps by F2L case. Sets which are subsets of others are indented, sets that have two different names are written on the same line.
Note that subsets which do not have a name are not shown here.
F2L 1 & 2 
F2L 3 & 4 
F2L 25 & 26 
F2L 32

F2L 33

F2L 34

F2L 37 
F2L 38 
F2L 39 
F2L 40 
Other subsets
The following shows other sets that are not restricted to any F2L case.
 ZBLS: Solves any pair and orients the edges.
 COLS: Orients the corners (not the edges) and solves F2L.
 OCLS: Orients the corners and solves F2L when edges are already oriented.
 Oriented LS: Orients everything when the last layer consists of only oriented pieces, except for the F2L ones.
 TSLE: Solves the F2L edge and orients the corners when edges are already oriented.
 OCLS: Orients the corners and solves F2L when edges are already oriented.
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 at least 864 algorithms, including mirrors.
 Because of the first point, this means that if the solver were to learn full VLS and HLS, it would take over a year to learn if 2 algorithms were learned per day.