Is there a way to look at data written into MCU registers?

Hi. I'm a newbie. Has anyone written an app, that allows you to see what is in the MCU registers,or to look at what is written in bootloader section of flash memory? Thanks. Rich.

EDIT: I think I need a debugger to look at register values and such. Seen one for STM MCU's associated with a development board. Not sure if there is an Arduino solution. Don't think so.

The AVRs have a debugging protocol, but it's proprietary, and not supported by the usual Arduino Hardware.

You can get something like the Xplained Mini Eval 328p board, which is almost like an Uno, but DOES have debugging support.
You'll need a debugger as well, like the ones included with "Atmel Studio 7" or "MPLABX" (downloadable from Microchip. 3-5GB each :frowning: )