pico2-debug runs on the (typically dormant) second core of a RP2350 MCU and provides a USB CMSIS-DAP interface to debug the primary core. No hardware is added; it is as if there were a virtual debug pod built-in.
Boot the RP2350 with the BOOTSEL button pressed, copy over pico2-debug.uf2, and it immediately reboots as a CMSIS-DAP adapter. pico2-debug loads as a RAM only .uf2 image, meaning that it is never written to flash and doesn't replace existing user code.
If this sounds familiar, pico-debug does the same thing, but for the RP2040.
With pico2-debug-gimmecache, 504kBytes (~97% of total) of SRAM is available for running user code; pico2-debug gives plenty of elbow room by occupying only ~3% at the very top of SRAM and leaving the flash cache operational.
If viewing this on github, pre-built binaries are available for download on the right under "Releases".
TinyUSB and code specific to pico2-debug is licensed under the MIT license.
ARM's CMSIS_5 code is licensed under the Apache 2.0 license.