Acorns

Acorns rounds up every purchase to the nearest dollar and automatically invests the difference into one of five diversified ETF portfolios based on your risk tolerance. There's no minimum investment required, making it ideal for students living on tight budgets who want real exposure to the stock market without large lump-sum commitments. The app links to a debit or credit card and handles all investing decisions based on your selected risk profile.

Works particularly well for those who forget to save manually or find investing intimidating. The set-and-forget approach means money flows into diversified holdings without any ongoing effort. It complements budgeting apps by automating the final step of capturing leftover cents.