Currently, the Dubai government has only ratified a tax on profits of branches of foreign banks and of all companies operating in the oil, petrochemical and gas sector. There are no taxes on capital gains, the capital itself and dividends.
However, in order to have a business in the UAE you need to pay an annual license fee (whose value depends on the type of business); and there are a number of other fees: the company may need resident visas for the entrepreneur, his or her family and their employees. Then, there is the newly-implemented EChannel (a sort of company registration needed to issue the necessary Immigration Card to issue visas). And from 4 February all those who want to apply for a new work visa must produce a certificate of good conduct that must be translated, certified and stamped by the proper Embassy and the Ministry of Foreign Affairs.
Most customs duties are very low and may even be excluded for certain categories of products like in the case of materials to be used for the production of goods to be re-exported. But in other cases they reach 100% of the value of the product (alcoholic beverages, energy drinks, tobacco).
Then, on 1 January 2018 the United Arab Emirates introduced VAT, whose input has far-reaching implications for companies that will need to make use of professional figures or service companies for their management. VAT is set at 5% but basic foodstuffs, education and health care will be exempt; in addition it will cover transactions involving the exchange of products or services within the UAE and with Saudi Arabia.
Taking a look at neighboring countries (in particular Qatar and Saudi Arabia), you can see that businessmen opening activities there need to consider the cost of setting up the companies, the possible share capital to be paid, the mandatory office that will pay 10% and 20% of taxes respectively on all that is generated with foreign countries. And even if all the generated income is foreign, a certified auditor needs to be accounted for. So today opening a business in a Free Zone is still your best bet (not requiring the visa requirement, physical office, accounting records, share capital to be paid).