Hello by default Odoo didn't provide the any such feature in Odoo V8.  

We suggest you once look at the App named Manage Sale Promotions in Odoo for the the general sales operation and Coupon Code in Odoo eCommerce  for the Website sales. For managing sale just like buy 2 and get 1 specific product free (All product is different type)  These apps are available in the V10 and V11. 

Here are some of the highlighting features of these apps:

Select  any of the following Promotion Levels

1) Global Discount - Applies to all products

2) Category Discount - Applies to specific product category or sub-category

3) Product Discount - Applies to specific product and all its variants

4) Variant Discount - Applies to specific product variants

Then, Select any of the following  Promotion Types

1) Fixed Price Discount

Apply flat fixed price discounts by specifying the exact amount.

2) Percentage Discount

Set specific percentage to offer flat discounts.

3) Range based Discount

Set discounts based on Price Range and Quantity Range.

4) Clubbed Promotion

Merge two promotional offers to provide additional discounts.

5) BOGO Offer

Configure Buy One Get One offer.

Other Features

• Set Promotion Duration by specifying start and end dates.

• Set overall promotion budget and specify maximum discount amount per sale.

• Auto Generate Promotion Codes or use your own code.

• Set minimum order amount or quantity of items in an order for promotion to be applicable.

• Set usage restrictions by configuring total number of times a coupon can be used and maximum number of times a customer can use a coupon.

• Configure promotions to make them available for specific customers or customer groups

• Create & Print Barcode/PDF for the Promotion

• Share Promo Code via email with customer.

• Create QR Code for the promotion and on scanning the QR Promotion will be automatically applied to your cart.   

You can check out these Apps named Manage Sale Promotions in Odoo for the the general sales operation and Coupon Code in Odoo eCommerce  for the Website sales.