In the case of fields with masks (CNPJ for example) and/or date, which ui free framework would be most recommended?
You can use the jQuery.Maskedinput, which can be used in conjunction with any of the above frameworks.
Use:
$("#Cpf").mask("999.999.999-99");
which ui free framework is most recommended for fields with masks, date (which opens the calendar), monetary,...
The question is based on opinions, but I will try to go on a more objective side.
For masks, jQuery Masked Input solves most cases.
For dates that open a calendar there are several options. A good option is the datepicker of jQuery UI.
For money, an excellent option is the jQuery Money Mask.
Example of use:
$("#Valor").maskMoney({
prefix:'R$ ',
allowNegative: true,
thousands:'.',
decimal:',',
affixesStay: false
});