PyAvrOCD is a GDB server that connects to all compatible Microchip debug probes (such as SNAP, Atmel-ICE, and even the DIY probe dw-link) and provides support for all 8-bit AVR MCUs (except XMegas), and it is integrated into the Arduino IDE. You only have to paste the right package URL into the Additional Boards Manager URL field. Then you can install or upgrade the appropriate board package. You can also use it in other IDEs or by using the CLI of GDB.

See https://pyavrocd.io for quickstart guides, a list of compatible debug probes, MCUs, boards, and board packages, and an extensive manual.