I use iSpy. Its free and open source and you can connect as many IP cameras to it you want. Need cloud backup? Save the videos to google drive. Need text notifications? Theres apis for that.
I had to dig really hard to find a link to github (https://github.com/ispysoftware/iSpy) but I get the impression from the README and lack of activity that this repo was superceded by another product from the same company, and that appears to be what the main website is marketing for download/payment. And according to the license file, some rather important bits of it are not open source at all.