Cuckatoo Cycle is a proof of SRAM. Cuckatoo32, as used in some cryptocurrency, requires 512MB of SRAM to solve efficiently (in addition to 512MB of DRAM).
The solution process is dominated by writing and reading of individual random bits.
Currently available Cuckatoo32 ASICs only have 64MB on-chip SRAM, causing an 8-fold reduction in efficiency, which still outperforms GPUs.