TL; DR

1. MS Windows – Use NHM Writer – Download Link

2. Any Browser on Microsoft OS – Use On Windows – Google Input Tools

3. Tablets and Phones On Android – I like Ezhuthaani app keyboard: Ezhuthani – Tamil Keyboard – Android Apps on Google Play

4. Apple iPhone, iPad, Phablet devices – Natively support Tamil input with Anjal (Amma = அம்மா) or Tamil99 keyboard layouts

Browsers

Mozilla FireFox

Use TamilKey extension – mozdev.org – tamilkey: index

Google Chrome

Use Tamil Input Tools from ChromeStore: Google Input Tools – Chrome Web Store

Apple Safari

Internet Explorer

Follow instructions for typing in Microsoft Windows

or use a installed application like NHM writer, eKalappai:

1. NHM Writer 2.0 | Indian Language Software Products & Services – New Horizon Media

2. eKalappai 3.0 can be downloaded in the following URLs:

• http://thamizha.com/project/ekalappai
• http://code.google.com/p/ekalappai/downloads/list

Android

Useful Link: ▶ How to replace your Android or iOS keyboard | PCWorld

Install one of the following Keyboards:

1. Sellinam – Android Apps on Google Play

2. Ezhuthani – Tamil Keyboard – Android Apps on Google Play

3.  Swype has Tamil language support. You even swipe along the keys to type which is much better and much needed input method for Tamil input. – Swype Keyboard Free – Android Apps on Google Play

4. ThamiZha! -Tamil Visai – Android Apps on Google Play

iOS

Binarywaves: How to Type Tamil in iOS7

Apple iPhone

Apple had added Tamil keyboards to its iOS 7 release

• Tamil 99 (Tamil Keyboard with Tamil Alphabets)
• Anjal (English Keyboard – with Phonetic Support for Tamil)

Microsoft Windows

In Windows 7 (as with most other operating systems) you can change both the language of the keyboard you are using to type things and the language of the visual interface. In this tutorial, I will show you how to manage the keyboard input languages on your system. This includes: how to add or remove a language, previewing the keyboard layout of a language, customizing the language bar and switching between languages.

More Info here

How to Add or Remove a Keyboard Input Language

All settings related to the keyboard input language are done from the ‘Region and Language’ window. There are several ways to find it. One would be to open Control Panel and go to ‘Clock, Language, and Region’. There you can either click on ‘Region and Language’ and then on the ‘Keyboards and Languages’ tab or directly on the ‘Change keyboards or other input methods’ link.

How To Add and Enable Tamil Languages in Windows

Windows 2000

Windows XP

Windows Vista

Windows 2000

To add an Tamil language in Windows 2000, follow these steps:

1. Click Start , point to Settings, and then click Control Panel.
2. Double-click Regional Settings.
3. Click the General tab, click to select the check box next to the Tamil language group you wish to install, and then click Apply. The system will either prompt for a Windows 2000 CD-ROM or access the system files across the network. Once the Tamil language is installed, Windows 2000 will prompt you to restart the computer.

To enable a newly added Tamil language and specify a Tamil keyboard layout in Windows 2000, follow these steps:

1. Click Start , point to Settings, and then click Control Panel.
2. Double-click Regional Settings.
3. Click the Input Locales tab.
4. In the Input Locales box, click Tamil language, and then click Properties.
5. In the Keyboard Layout box, click the Tamil keyboard layout, click OK, and then click OK.

Internet Explorer Administration Kit (IEAK)

The Tamil language support for text display and text input can be included when you create an IEAK package for Microsoft Windows 98, Microsoft Windows Millennium Edition, and Windows NT clients. This occurs in “Stage 2 – Automatic Version Synchronization” of the IEAK Customization Wizard.

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Windows XP

To install Tamil language and Tamil keyboard layout in Windows XP, follow these steps:

1. In the Windows XP standard Start menu, click Start , and then click Control Panel.

   In the Windows XP classic Start menu, click Start , click Settings, and then click Control Panel.

2. Double-click Regional and Language Options.
3. Click the Languages tab, and then click Details under “Text Services and Input Languages”.
4. Click Add under “Installed Services”, and then click Tamil language and the Tamil keyboard layout you want to use for that language.
5. To configure the settings for the Language bar, click Language Bar under “Preferences”.

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Windows Vista

1. Open Regional and Language Options by clicking the Start button , clicking Control Panel, clicking Clock, Language, and Region, and then clicking Regional and Language Options.

2. Click the Keyboards and Languages tab, and then click Change keyboards.

3. Under Installed services, click Add.

4. Double-click Tamil language, double-click the text services you want to add, select the text services options you want to add, and then click OK .