So many gadgets purchased over the years, and many of them really useful (others not so).
Back when my children were small I would have said, without hesitation it was my large Hi Dome Pressure cooker. Used all the time, for tenderising cheap cuts of meat, making james and marmalades, steaming marmade puddings, etc., making soup.
Of course, all these things now done in easier to use machines.
MIcrowaves have made a huge difference to my life, and I now have a wonderful combi one, which has replaced the need for a large oven.
Electric mixers, taking away that long, very difficult process oc creaming together butter and sugar at the start of sponge making.
BUT.....back to basics, pretty sure the machine I would not want to live without is my washing machine.