Let me show you some tools or possibilities which can be used to write in Devanagari (देवनागरी),  the standard script for Hindi. I have found two possibilities for the same, one is online websites or services and offline software which you can install on your computer to writing directly to your favorite text editor such as Microsoft Word, Notepad etc.

To write in Hindi, you must know the romanized Hindi. Romanized Hindi is formed when you replace the alphabets in Hindi with their similar sounding alphabets in another language. For example, if you want to write “नाम” (Eng. Name) then its romanaized Hindi spelling will be “Naam”. When you write this romanized spelling (“Naam”) into below mentioned tools, the romanized spelling will be transliterated (not translated) to “नाम” (in Devanagari script). Here we should remembers that there is no standard rules which defines the romanaization of Hindi. The best bet would be to use the form which will transliterate into the right word in Hindi i.e. Naam transliterate to “नाम”, but Nam would not.

Online Tools:

Online tools can be used by accessing the website and you can write into the specified field in romanized Hindi, while the transliterated message appears in the other field. You need to select the target/translated language to Hindi. In Google Input, however, you are presented with 0nly one field where you write in romanized Hindi and it is instantly transliterated to Hindi as soon as the word is completed.

If you’re interested in using any of the online services, please visit the links below (all services are free to use):

1. Google Input

https://www.google.com/inputtools/try/

2. Google Translation:

https://translate.google.com

3. Quillpad

http://www.quillpad.in/index.html

4. Web Dunia Utilites

http://utilities.webdunia.com/hindi/onlinetypingtools.html

Offline Tools:

There are some software that you can install on your computer and start typing in Hindi in a text editor (Microsoft Word, NotePad and etc) . If interested in using any of the offline tool, please visit the links below (all softwares are free to use):

1. Microsoft Indic Language Input Tool

http://www.bhashaindia.com/ilit/HindiPreInstall.aspx

2. Google Hindi Input Tool

http://www.google.co.in/inputtools/windows/