SMMS (Scholey - McNeill Multi-Slotting), commonly called F <RU> F', is a F2L technique proposed by Jayden McNeill and George Scholey in late 2019. The core concept is to solve the BR>FL (or FR>FL or sometimes FR>BR>FL) pairs simultaneously by starting with an F and finishing with an F' move, while <RU>-gen turning is performed in between. It allows for fast, rotationless and nearly 2-gen solving and is commonly used in combination with the CFOP method.
Jayden McNeill posted a video about this concept on October 31st, 2019. The approach he outlined in said video is an upgrade of an earlier idea he had for solving the FL pairs in an F <RU> F' manner, about which he had posted a separate video back on January 11th of the same year. In the initial stage, solving cases in this manner with the FL edge oriented couldn't be accomplished in a convenient way due to requiring a y2 rotation.
To adress this issue, Jayden McNeill generated algorithms for solving these cases and realized that using this approach, the issues of recognition and the practicality were resolved. This turned into a viable way to solve F2L in CFOP.
Simultaneously, George Scholey came up with a different way of solving F2L in a similar manner: Performing an F move, solving BR and FR with <RU> moves and finishing with R' F' R.
To make this more practical, Jayden McNeill then came up with JSS (Jay Second Slot) where one solves the FR pair by creating a joint pair in such a way that the BR edge becomes oriented, so that the rest of the F2L can be solved in a F <RU> F' manner.
To further improve on this concept, work is currently being put into solving more EO cases and forcing OLL skips.