Moonn or MAS have the BazzFuss on a teensy PCB, I forget which — maybe both. Great fuzz, underrated.
There's also the G.B.O.F board from GuitarPCB — numerous simple 1- and 2-transistor circuits can be made upon the GBOF such as Fuzz Face, LPB-2, Duende Boost, Electra, aforementioned BazzFuss, Ehm-drive etc.
GPCB's Zenith Mini gets you bufferless-YATS such as the Timmy, LDO and similar.
Some tiny boards can be had from Delyk PCBs.
The Lawn Darts from Effects Layouts is about the size of a postage-stamp, build the EQD Arrows on it or mess around and mod it to something else.
PPCB's Two Sticks of Derm...
Lotsa cool stuff out there. Have fun.