Unicode Fonts

For texts in Latin script, you might want to check the free Brill or Junicode fonts that have extensive diacritical coverage. For more options see also Medieval Unicode Font Initiative, SIL Unicode Fonts or Open-source Unicode typefaces on Wikipedia.

Tamil

Recommended reading:

• Mello Vargas, Fernando de. Evolution of Tamil typedesign: Origins and development (MA dissertation). University of Reading, 2007.
• Maheswari P, Uma. Advent of Print Culture in Colonial Tamil Region: Technological, cultural and social challenges from 1712 to 1947 (PhD thesis). Pondicherry University, 2013.

Font developers: Developing OpenType Fonts for Tamil Script

Built-in Windows Fonts

Starting with Windows 10, all bult-in Tamil fonts apart from Nirmala UI have been moved to an optional feature. To enable these additional fonts, go to Settings > Apps > Apps & features > Optional features > Add a feature and install Tamil Supplemental Fonts.

Font Name	Basic Block	L2/01-375R Symbols	L2/03-273 SHA	L2/04-073 Zero	L2/06-184 Om̐	L2/17-069 Supplement	Availability
Nirmala UI	●	●	●	●	●	○	since Windows 8
Vijaya	●	●	●	●	●	○	since Windows 7
Latha	●	●	●	●	●	○	since Windows XP
Arial Unicode MS	●	○	○	○	○	○	Office 2000-2013

Google Noto Fonts

Google Noto is a set of free fonts from Google, aiming to support all languages with a harmonious look and feel. Installation instructions here.

Font Name	Basic Block	L2/01-375R Symbols	L2/03-273 SHA	L2/04-073 Zero	L2/06-184 Om̐	L2/17-069 Supplement
Noto Sans Tamil	●	●	●	●	●	○
Noto Sans Tamil Supplement	○	○	○	○	○	●
Noto Sans Tamil UI	●	●	●	●	●	○
Noto Serif Tamil	●	●	●	●	●	○
Noto Serif Tamil Slanted	●	●	●	●	●	○