This list is compiled from different people's suggestions and tips, as well as some asking and searching around. It is updated every now and then to remain current, weed out errors or add information. If you have suggestions, updates, comments or additions to this list, you're welcome to comment here, post something in !thrifty or in !frugal, or DM me.

Worldwide (or available in several countries)

• Too good to go - App-based service that allows restaurants and stores to post unsold surplus food or produce. Very popular, even though the food or produce you get is often random and it can sometimes run out before you manage to pick it up. Currently available in: Austria, Belgium, Canada, Denmark, France, Germany, Ireland, Italy, Norway, Poland, Portugal, Spain, Sweden, Switzerland, The Netherlands, United Kingdom and parts of the United States
  [Apps for iOS, Android and Huawei are available from site]
• Phenix - App-based service similar to "Too good to go". Currently available in: France, Réunion island, Guadeloupe islands, Martinique island, Spain, Portugal, Belgium, Italy and Hong-Kong
  [iOS apps are country specific, check the site] - [Android app]
• Olio - App-based service with freecycling only, both food and items from individuals and companies (like bakeries). The app is supported by third-party ads, there is a paid subscription to remove ads.
  [Apps vary depending on country, see site]

Canada

• Flashfood - App-based service that allows grocery stores to post unsold surplus that can be bought for a fraction of the original price. Also available in some US states.
  [iOS app] - [Android app]

Denmark

• yourLocal - App-based service that allows restaurants and stores to post unsold surplus food or produce. It also makes it possible for individuals to share surplus food with other people in their neigbourhood.
  [iOS app] - [Android app]

Germany

• Mundraub - An initiative to map out free-to-pick fruits, veg, herbs and nuts. Mainly in Germany.
  [Android app]

Poland

• Foodsi - App-based service that allows restaurants and stores to post unsold surplus food or produce. The food is supposed to be discounted at least 50 % of the original price.
  [iOS app] - [Android app]

Portugal

• Fruta feia - This ("ugly fruits") is a cooperative that collects fruits and vegetables that are too small/large or misshapen, and sells them in really affordable boxes.

Spain

• Gratix - A freecycling app that has karma-based self-moderation. According to some sources, people can also give away food freely(?)
  [iOS App] - [Android app]
• Panduru - This is a food waste reduction initiative, where they take surplus bread from bakeries and turn them into pastries that they sell. Currently available in Asturias. Unsure if it's relevant for thrifty/frugal, let me know.

Sweden

• Karma - App-based service that allows restaurants to offer unsold surplus meals at a discount. Currently only used in the major cities(?)
  [iOS app] - [Android app]
• Matsmart- Online grocery store that collects surplus or unsold food items and resells them cheaper.
  [iOS app] - [Android app]

United States

• Flashfood - App-based service that allows grocery stores to post unsold surplus that can be bought for a fraction of the original price. Also available in Canada.
  [iOS app] - [Android app]
• goMkt - App-based service that allows restaurants to offer unsold surplus meals at a discount. Is this site still active? The apps are not available in App store or Play store any longer.
• Hungry harvest - Collects surplus or unsold produce and resells them in affordable boxes, they also make preserved items from some produce. Currently available in: Maryland, Washington, DC, Greater Philadelphia, Southern New Jersey, Northern Delaware, and Raleigh, North Carolina
• Imperfect foods - Online grocery store that collects surplus or unsold food items and resells them cheaper. Also has cheaper produce with quirks or irregular shapes and sizes. Works together with Misfits Market.
• Misfits Market - Online grocery store that collects surplus or unsold food items and resells them cheaper. Currently available in 48 states, except for Alaska, Hawaii and Puerto Rico.
• Food rescue US - Connects volunteers, food donors, and social service agencies to ensure that surplus food reaches people who need it most. Unsure if it's relevant for thrifty/frugal, let me know.
• Food rescue hero - A network that connects donors who have fresh, highly perishable food that would otherwise be thrown out to the people who need it most. Seems REALLY similar to Food Rescue US, unsure if it's relevant for thrifty/frugal, let me know.