Just remember there are usually three reasons you are making this. For the challenge (yourself) For money (public) ordered-list When you pick the project youre going to do determine who youre trying to make this for. I used to do this with a friend of mine once a year during college where we would take on an insane project within a short period of time. OFFICE Notepad Microsoft Office Add-on Adobe Acrobat Plugin Spreadsheet editor Power BI visualization Painting or Photo editor Photoshop Plugin Image palette GIS mapping tool (based on MapBox or Google Maps) PS. ignore zip codes and counties as it can drive you crazy Translator NETWORK Website Non-profit 1 School or educational service 1 Military 1 Fire department 1 Human rights 1 Emerce 1 Search engine 1 Hot or Not 1 Forums 1 CMS Plugin Quiz designer app Online & offline (Gzip & 7zip) clone RSS feed IRC clone Online & SMS Messenger Peer sharing Social media management system Web framework Simple anti-virus Simple firewall & network management GAME DEVELOPMENT Pong Pac-man Tetris Mega Man Legend of Zelda Super Mario Bros Contra Flappy Bird Angry Birds Ikaruga Braid FPS mod Games not to try in 72 hours from scratch AD&D Wolf or most pen & paper RPGs Most table top games 2D RPG You could get a visual grid in 72 hours. 1 You can make a working DB system in 72 hours. 1 You could get a primitivebat system in 72 hours. 1 Can do whole thing well in 72 hours. If someone reading this can please post on Twitch or YouTube and Ill watch. 1 Doom or 99% of FPS games. Mathematics Algebraic calculator with steps Graphing calculator Dietary needs calculator Exercise calculator Ray Tracer Decision Making To do list or project management suite Fitness bot Webined the dietary needs & exercise calculator together to make it estimate what people should eat and what exercises to use 1 Financial portfolio AI Chat bot Interpersonal and conflict resolution strategies Political strategy like NationState or Filteries Personal Management System Answer retrieval system Information Management