The most interesting exotic numeral systems I know of are Cistercian numerals [1] and Indic [2] and Ottoman [3] Siyaq numbers. The latter two were even added to Unicode 14.0 [3][4], but not many fonts support them.
[1]: https://en.m.wikipedia.org/wiki/Cistercian_numerals
[2]: https://en.m.wikipedia.org/wiki/Indic_Siyaq_Numbers
[3]: https://en.m.wikipedia.org/wiki/Ottoman_Siyaq_Numbers
[4]: https://unicode.org/charts/PDF/U1ED00.pdf
[5]: https://unicode.org/charts/PDF/U1ED00.pdf