Considering other prominent cryptocurrencies besides Bitcoin, the currency that stands out with a very low maximum number of units is Litecoin ($LTC ), although its number is still higher than Bitcoin.

Maximum supply: The maximum supply of Litecoin is only 84 million units.

Comparison: This number is still very low compared to the hundreds of billions or trillions of other popular currencies like Ripple ($XRP ) or Dogecoin ($DOGE ) or Shiba Inu (SHIB).

Current supply: It is currently being mined, with approximately 74.6 million coins in circulation.

Design: Litecoin was designed to be the "digital silver" compared to "digital gold" (Bitcoin), with slightly faster transactions, while maintaining relative scarcity in the number of units.

Relative scarcity: The cap of 84 million units makes it one of the most scarce major cryptocurrencies in terms of total available supply.