Not really a gadget, but more if a useful tip…………. If you need to wring out a dishcloth, for example, loop it round your kitchen tap and twist the loose ends round and round. You are obviously using your painful hands, but the results are better and quicker than what you could achieve with the more traditional method.
I was advised to do this when in hospital over 40 years ago when first diagnosed with RA. Also, I wonder if you are resting your hands in the rather fetching black “mittens” which you will get through the hospital. I find these really useful. Years ago they were ugly beige things with Velcro fastenings and metal strips , but now they are tight fitting, stretchy black material with a zip.
I would recommend an electric tin opener, but with any knife or gadget with a handle, go for the chunkiest one, slimmer ones are more difficult to grip - they tend to send my hands into a spasm. I would also endorse everything recommended by lixy, I have found that the simplest solutions are often the best.
Arthritis is cruel and particularly frustrating in the hands.