This is an OverDrive processor for an additional OverDrive socket on the mainboard.
Upgrades 25 MHz Intel 486SX based systems to 50 MHz.

Note the extra pin. It is a kind of "tell the other guy to shut down" pin. Implemented so that the end-user can just "add" this new chip into the spare upgrade socket, without any need of interfering with the originally supplied SX CPU. Ie. what end-user can remove a PLCC or even PQFP chip.

The 80387SL is a coprocessor designed for use in systems based on an Intel 386SL CPU. The 386SL is derived from the 386SX. It is a static CHMOS IV design with very low power requirements that is intended to be used in notebook and laptop computers.

The 387SL, introduced in early 1992, has been designed to accompany the 386SL in machines with low power consumption and substitute the 387SX for this purpose. It features advanced power saving mechanisms. It is based on the 387DX core, rather than on the older and slower 80387 core (which is used by the 387SX).

Upgrades 33 MHz Intel 486DX and SX based systems to 66 MHz.

T type: Extended temperature range (-40°C to +85°C)

Upgrades 25 MHz Intel 486DX and SX based systems to 50 MHz.

First CPU specifically designed for Notebook PCs.

The last i486 with core frequency equal to bus frequency, introduced in June 1991. It was followed 1992 by the DX2 with clock doubled core frequency.

To run it at its 50MHz, this Intel chip demands a heatsink. To over-clock this chip, it demands a heatsink-fan (purpose designed for the later DX2 -66 {and hotter} chips). I overclocked the only one I ever bought. It ran at 60MHz all day long. (with the heatsink-fan of course). I failed to overclock it at 66MHz. I never knew whether it was the m/board chipset chips, or the -50 CPU that failed at 66MHz. Could have been either, since the chipset chips were also stamped -50.
 
For a long time, Intel only supplied samples of the i486DX -50 CPU to OEMs. This went on for nearly one-year. The 50MHz M/Board was a real "trouble-maker" at the time, and no 50MHz supporting chipsets had ever been in use before this time. Until then, less reputable OEMs had made 4-layer M/Boards alongside the more-expensive 6-layer M/Boards. This had the double-expense to these low-grade OEMs, of needing to make 6-layer boards only, for 50MHz operation throuhgout, and to source expensive 50MHz supporting chipsets! With Intel's long holdup of commercial volumes of -50 CPUs, these nasty OEMs had time to re-develop stable 50MHz M/Boards. However, one-year later when consumer 50MHz 486 systems flowed freely in the marketplace, many "clones" were still very unstable, due to 4-layer designs persisting still, and due to non-use of a heatsink on the CPU (as extra cost-cutting)!!! The -50 was the first x86 CPU to demand a heatsink. N.B. the later-on i486DX2-50 did NOT require a heatsink, but usually came fitted with one anyhow. (I guess the system builders had gotten used to fitting heatsinks by now).