Source Sans Pro

Source Sans Pro brings a distinct rhythm to layouts where the details of a letterform matter. In the BeauFonts catalog it is grouped as a sans serif family, with 6 listed weights: 200, 300, 400, 600, 700, 900. The best way to judge it is in context: set a short heading, a sentence of body copy, and the key labels around it.

For language coverage, the source lists cyrillic, cyrillic-ext, greek, greek-ext, latin, latin-ext, vietnamese. That information is useful when a design includes more than basic Latin text, but a final build should always be checked against the actual characters, punctuation, and symbols you plan to publish. Source Sans Pro can be explored here as a working specimen: adjust the size, compare the listed weights, and copy the generated CSS only after confirming the source license fits your use.