Yums are the 'currency' of restaurant website The Fork, available in a fair number of European countries. Use this link to sign up and make your reservation. When you do so, you get 1000 yums, 'worth' 20 euro in discount. I get 500 yums if you use the link and honour your first restaurant reservation.
The Fork lets you book a table easily. You can always cancel if you change your mind. Note that the restaurant owner pays for the booking. Last time I checked every reservation costs them 1,50 euro. The yums you earn can be used for discount (1000 yums = 20 euro, 2000 yums = 50 euro).
This discount cannot be combined with other offers. Many restaurants offer a percentage of your bill as a discount, varying from 20% to 50%. Sometimes the discount only applies to food items, and not to menus. Restaurants not honouring the discounts are very rare in my experience (I had one occassion only in recent years).
Please be aware that yums are a currency that is entirely paid for by restaurant owners. The restaurants that accept yums in return for discount only get a 50% discount on their The Fork cheque in return, insofar as I could check.