There are no completely free alternatives as far as I know. It costs a fortune to develop and train the AI and then running the servers requires a team of sys-admin and security personnel, as well as beefy hardware and bandwidth. It’s not possible to sustain a business like that for free.
ChatGPT is free as is Microsoft Bing. There is no telling how much longer that will be true. Microsoft Edge has a pointer to Bing at the top of its right sidebar.
I briefly tried “freedom gpt”, which you can run locally on your PC, but it sucked arse. It was about as bad as a first generation chat bot from 20 years ago.