It is quite similar to a deposit placed in a bank or any other financial institution except that a company fixed deposit is "unsecured". Fixed  Deposits  earn a fixed return which is fully taxable unlike interest on bank deposits & other investments (which are covered under section 80L of the Income Tax Act). However no tax is deducted at source upto an interest income of Rs.2500/- per annum. Moreover, if the depositor submits form 15H , no tax is deducted at source, even if the interest amount exceeds Rs.2500/- per annum.
You may place deposits in manufacturing or finance companies but ensure that such FD schemes are rated by credit rating agencies like Crisil, Icra, Care or Duff & Phelp.

Request for Fixed Deposit Forms

Also for Karvy Fixed Deposits

Click here for the list of Finance Co. FD schemes

Click here for the list of Manufacturing Co. FD Schemes