I Am Not A Lawyer, But...
There's a fairly large precedent set by https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Microsoft_Corp. stating that the overall "look and feel" of a piece of software is not copyright-able, only very specific attributes thereof (and maybe not even then?). So, theoretically something like "Financier uses a lightning bolt icon for monthly options" could be something they could try to sue over, but "Financier looks a whole lot like YNAB" is not.
There's a fairly large precedent set by https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Microsoft_Corp. stating that the overall "look and feel" of a piece of software is not copyright-able, only very specific attributes thereof (and maybe not even then?). So, theoretically something like "Financier uses a lightning bolt icon for monthly options" could be something they could try to sue over, but "Financier looks a whole lot like YNAB" is not.