Clone http://neonmob.com:
It’s a digital art collecting and trading website.
The neonmob community would thank you for an open source version 
For current pain points: http://forum.neonmob.com/t/please-bring-back-the-old-neonmob/3025/2
Preprocessing as a service website:
Hooks into a user’s code repos, and preprocesses their jsx, coffee, typescript, sass, less, pug, etc. files and exports the artifacts to a location of the user’s choice.
Other angles you could do is to preprocess the files and report syntax errors or code smells for the user to inspect. Going further, you could create a bot that makes pull requests with edit suggestions.
Unit test logging dashboard:
Provision API credentials to users to post unit test results from services like Travis CI, Gitlab CI, etc. Then display the data in a dashboard. Going further, you can set up push notifications when new data is posted. Other opportunities here could be to visualize the errors or traces in a unique way that helps the user find the root cause.
Sports analysis service:
Allow users to upload replays of gameplay. Add an overlay tool that allows tacticians to mark up the video or make comments. Going further, you can track player stats over time to construct a profile of strengths and weaknesses.
Code similarity screener:
A light plagiarism checking tool that indexes code on the web. Allows users to upload code and check for similarity to pre-existing solutions based on algorithmic similarity.
Gift Bundling app:
Help users search gift items on amazon and save them into gift bundles. Gift bundles are groups of items that make sense as a gift basket. Let users tag gift bundles for different occasions (birthday, wedding, anniversary, graduation, etc.). Let users search public bundles by filtering total price or intended event and vote on their favorites. Going further, track price changes for bundles as a whole and alert users when the bundle price dips below a threshold. Going further, generate a thumbnail or cover image for bundles and let users post bundles with details to Pinterest.
Env Manager:
Know that pesky .env file that is sometimes forgotten to add into .gitignore? Eliminate it entirely by creating a web app that allows users to manage permissions and validity duration of their credential variables. Publish a start script as an npm package that users can add into their app as a dependency. Then they can start their app and inject environment variables from your server (instead of $ node app.js it would be $ [package name] app.js). The server would still have to provision access keys.
Node.js CMS:
Self-explanatory. Make a simple MVP though. Going further: add hosting as a service.
Database Service:
Create a key-value storage service by implementing a subset of Redis’s commands: SET, GET, DEL, EXISTS, DBSIZE. (Other source of inspiration for a command set: https://www.thumbtack.com/challenges/simple-database). The front end web app allows a user to provision and manage instances, and view or regenerate API keys and connection strings. Either publish a package that interfaces with the service through a connection string (e.g.: service://user:pass@service.herokuapp.com/collection_name) or expose the endpoints through an ID (e.g.: https://service.herokuapp.com/instancehash/dbsize).
Free Food Finder:
Crawl university calendars, meetups, etc. to find events that offer free food. Then aggregate the results and present a simple index for the front end.
Build an MVP of a Heroku add-on: https://elements.heroku.com/addons
Tier 4 projects from @P1xt’s guide are good too: https://forum.freecodecamp.com/t/computer-guide-web-development-with-computer-science-foundations-comprehensive-path/64516
Or complete the triple certification and get a non-profit client project.