The Format Number API module provides a method to configure number formats (site default and user defined) with configurable decimal point and thousand separators. It's the same concept behind letting users choose a date format or timezone, but applied to numbers.

Several functions are exposed by the module that can be used by other contributed or custom modules to display numbers accordingly, from PHP and JavaScript as well.

External references:
- PHP manual: number_format().
- Unicode Locale Data Markup Language (LDML).
- Unicode CLDR Project: Common Locale Data Repository (CLDR).
- CLDR By-Type Chart: number.symbol.
- Wikipedia: Decimal separator.