It is one of the oldest members of the Indo-European language and with literature going back via Vedic Sanskrit to approximately 1400BC, Sanskrit has been key to the reconstuction of proto Indo-European.
The sacred Hindu texts (the Vedas) were written in Sanskrit, and it always been considered as high or literary language. Nevertheless it is still a living language and spoken in some villages in India.
Sanskrit is written using the Devanāgarī (देवनागरी) script. Some of the many languages using Devanāgarī are: Hindi, the Prakrits and Kashmiri.
The days being spoken in Sanskrit.
Sanskrit varta contains articles on learning Sanskrit, Hindi and other regional languages. Sanskritvarta.com