Robo-advisors have quickly grown to become a potent force in the financial planning marketplace. These automated programs are able to perform many money management functions, such as asset allocation, dollar-cost averaging, portfolio rebalancing and tax-loss harvesting at a fraction of the price that most human advisors charge.

Traditional banks and money managers are hurrying to get in on the act. Many are either looking to purchase or are developing their own robo-platforms in order to stay competitive. For investors seeking an automated solution to their financial decisions, or advisors looking to stay informed, here's a list of the most commonly used robo-advisors and how they work.

Companies With Robo-Advisor Services

1. Acorns: This robo-advisor only comes as a smartphone app where users input their personal information, link up their bank account and credit card, and choose from one of five portfolio models ranging from conservative to aggressive. Then the app rounds all of their purchases up to the nearest dollar and invests the difference in the portfolio.

2. Asset Builder: Developers designed this robo-advisor for long-term investors and uses mean-variance optimization to create buy-and-hold portfolios that are better able to weather bear markets. The service uses Dimensional Fund Advisors funds, smart indexing, and graded portfolios.

3. Betterment: One of the pioneers in the industry, Betterment automatically funnels investor money into an appropriate portfolio with investments that are designed to maximize returns and minimize risk using Modern Portfolio Theory, and they have human advisors available to provide more personalized advice.

4. Blooom: Focusing exclusively on managing money for defined-contribution retirement plans, this robo-advisor combines automated money management services with human advisors in order to provide a more complete range of services for its participants. It has a tiered pricing structure that is on the high end of the scale for small accounts.

5. Charles Schwab Intelligent Portfolios: This robo-advisor provides an automated money management service that employs over 50 exchange-traded funds (ETFs) from its large base of in-house investment offerings as well as third-party ETFs including Vanguard, iShares and Invesco. Schwab prioritizes ETFs that have the lowest operating expense ratios. It also uses its own technology platform and is a self-clearing service. There is a $5,000 minimum investment.

6. Ellevest: This platform has been designed specifically for women, with their unique lifetime salary curves, longer lifespans, and gender pay gap. It invests for women in a way to help offset these differences. There is no investment minimum and fees are very low (0.25%).

7. E*TRADE Adaptive Portfolio: Adaptive Portfolio creates diversified portfolios using either all ETFs or a mix of ETFs and traditional mutual funds. Portfolios are constantly rebalanced in accordance with E*TRADE Capital Management’s portfolio allocation drift parameters.

8. Fidelity Go: Fidelity's offering is designed to appeal to Millennials and has a $5,000 minimum balance. Portfolio rebalancing is done by investment managers on a non-deterministic basis. Investor money is placed into a combination of BlackRock and Fidelity Investments ETFs. It does not offer tax-loss harvesting services.

9. Financial Engines: Another platform that combines automated investing technology with human advisors. This company focuses on providing comprehensive financial advice and investment management to corporate employees in the workplace.

10. Financial Guard: This robo-advisor differs from its competition by charging a flat fee for its services instead of a percentage of assets under management or a fee for premium advice. However, it does not offer automatic portfolio rebalancing.

11. FutureAdvisor: FutureAdvisor offers direct investment management based on Modern Portfolio Theory. It is available through Fidelity and TD Ameritrade accounts. Investors pay the usual fees for using these accounts in addition to the fees charged by the platform. It invests mostly with Vanguard and iShares ETFs.

12. Hedgeable: Built for a more sophisticated investor, this robo-advisor and its investment portfolios are designed to cushion the blow from severe bear markets. It employs tactical security selection and also offers alternative investments such as private equity, bitcoins, and real estate and commodities.

13. LearnVest: Originally targeted to women, this robo-advisor has moved away from a gender-specific model. This site allows users to sync up all of their other accounts to get a comprehensive snapshot of their current financial position. There is also an advice and education center.

14. MarketRiders: This robo-advisor concentrates on serving retirement savers age 45 to 65 who want to make their own investment decisions instead of handing their money over to a money manager or mutual fund. The site provides resources that can help do-it-yourself investors make better decisions. Ready-made portfolios are also available. It charges a flat monthly or annual fee for its services and has a $25,000 minimum investment.

15. Merrill Edge Guided Investing: Bank of America's Merrill Lynch launched a robo-advisor service that combines the capability of Merrill’s online platform with the expertise of its investment advisors to drive investment decisions.

16. Motif: This platform allows users to invest in a basket of stocks called "motifs" based on themes and to customize asset allocation models by adding or removing securities, varying asset classes or changing their portfolio weights. It doesn't charge any advisory fees but flat fees of $4.95 or $9.95 for different trades. 

17. Personal Capital: This site targets aspiring wealthy people, who have $25,000 to $3 million in liquid assets. It offers a comprehensive financial tracking tool for all of the user's financial accounts and also a paid advisory service. Its retirement planning module also allows users to determine their level of preparedness for retirement.

18. Rebalance IRA: Launched as an affiliated service of MarketRiders, it specializes in retirement investing targeted at people between the ages of 45 and 65. In-person consultation sessions are available with investment advisors who use in-house software to rebalance portfolios. An account minimum of $100,000 is required at an annual fee of 0.5% based on the total assets under management.

19. SigFig: This algorithm-backed portfolio allocation platform optimizes risks, diversification benefits, and tax implications. It also automatically rebalances the portfolio shifted by market fluctuations and reinvests dividends earned. The minimum balance is $2,000, and the annual fee is free for the first $10,000 and 0.25% on amounts invested after.

20. Stash: The Stash iPhone app offers a variety of ETF portfolios customized for different themes, including social media, green tech, defense industry, and Warren Buffett holdings, etc. A monthly fee of $1 is charged for account maintenance (free in the first 3 months) without additional commissions or trading fees.

21. TD Ameritrade Essential Portfolios: This robo advisor product by TD Ameritrade invests in ETFs and offers automatic portfolio rebalancing, reallocation, and investing functions. It requires a minimum deposit of $5,000 and charges 0.3% advisory fee. 

22. Vanguard Personal Adviser Services: Vanguard introduced this new investment offering that uses primarily Vanguard funds and combines both a human financial advisor and robo-advisor services. Account minimum is $50,000, but the account management fee is only 0.3%.

23. Wealthfront: Wealthfront is a platform that focuses on tax-efficient investing and holds investor accounts at Apex Clearing Corporation. It uses index ETFs for its investment vehicles and also allows users to sync up their other accounts and receive investment advice on external accounts. Wealthfront is one of the cheapest robo-advisors in the business.

24. WiseBanyan: WiseBanyan touts itself as the "world’s first free financial advisor" without charging any account management fees or trading fees with no minimum balances. Fees are only charged on opt-in services and investment strategies. Investment accounts offered include personal investment accounts, Roth IRAs, Traditional IRA, and SEP IRAs.