MSP-EXP430G2ET is with eZ-FET lite (based on MSP430F5528/9) that can be used with any offboard TI MSP430 SBW (JTAG is not supported) target device. Beside breakpoint debugging, there is MSP-Flasher CLI (open source) that can be used on any OS too.
All TI FET's are open software / hardware, but replicating them will be more expensive than buying original one. MSP-UIF was replicated, but for today use it is too slow. MSP-FET use FPGA for interface to target device that is closed. But, again if you check part list, doubt that replicating will put price down.
For example, I bout 5529 LP that is at mouser right now 17 euros, and 5529 itself cost 11 euros, and on LP you have 2 (5528 is identical to 5529 except pinout). 5529 LP you can transform to 2 FET masters (one original and another on target 5529 device) using one USB cable.
Why nobody till today didn't port open source TI FET firmware from 5528/9 to bluepill or recent rp2040 (to boost speed for no cost). Don't know (no enough motivation for this). TI right now working on (porting to) new MSP-FET that will be based on ARM but it is unknown if it still be open source.
So there is not existing any low cost 3rd party product like LP. Only professional / expensive like Elprotronic.