I don't do it anymore, but back when I was 2boxing, I'd just use this Microsoft software, Mouse without borders: https://www.microsoft.com/en-us/download/details.aspx?id=35460
Used it on both Agnarr and Phini.
Pretty much anything with a celeron processor or better, 8 gb of ram, and an ssd would be fine. You can get a NUC barebone kit add 8 gb of ram, and a ssd for about 230 dollars.
I rack mount mine with this.
http://www.myelectronics.nl/contents/nl/d358_NUC_MiniPC.html
There's software that does the same thing. https://symless.com/synergy
And it's not against ToS.
But a KVM switch is a hassle but would work.
At the start of phinny I tried a KVM switch and switching back and forth every fight was just a pain in the ass.
Here's another option. It's a bit older and slower. Same situation with being a referb. Less reviews and lower ranked reviews than above.
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How do you feel about this:
AOSON R105 10.1-Inch Windows 10 Home OS Tablet PC Intel Atom x5 Cherry Trail Z8300 Quad-core 4GB RAM 64GB Storage 800x1280 IPS Touch Screen with HDMI 5000mAh Detachable Keyboard included Dark Gray https://www.amazon.com/dp/B01LF6SRFC/ref=cm_sw_r_cp_api_83dszb2SSR47W