Stash is a great micro investing app for those who want complete control over their investments. The app does not charge any fees or commissions on trading, and any other fees are published clearly on their app.
Acorns is another micro investment app that focuses on contributing small amounts to different investment portfolios. Depending on your risk level and investor profile, you can pick one of five diversified portfolios.
They focus on socially responsible ETFs, and offer a team of advisors to help users throughout the process if necessary. Their passive approach to investing and higher returns means their investment app is one of the most highly rated ones.