Is the money paid to subscribe to a website that gives a daily percentage for browsing other websites considered usury (riba)? Is browsing these sites and placing them at the bottom of the browser considered cheating? Is selling a product that creates websites similar to this work unlawful (haram)? And am I sinful if some of these websites are hosted by me?

It is not permissible to deal with this company for the following reasons:

The company requires merely accessing websites to make users believe that its sites are frequently browsed. This is deception and forbidden fraud. The amount paid is a loan guaranteed to be repaid with a specific increase conditioned upon accessing the websites. This is blatant usury (riba). A loan is "transferring ownership of a thing on condition that its equivalent be returned," and if an increase is stipulated therein, it becomes usurious. Even if this work were considered an ijara (leasing/hiring contract), it would be a void ijara because the compensation is not specified and is a percentage of an unstable amount, falling under the category of "two sales in one sale," which is forbidden by Islamic law. It constitutes an ijara conditioned on a loan, which is void like a sale. Ijara is a sale of usufructs, and it is invalidated by conditions not required by the contract. The contracted benefit is not considered valid under Islamic law.

Based on the above, it is not permissible to work within this company's system or promote it. Any wealth acquired from this work must be disposed of by spending it on the interests of Muslims, because it is illicit gain.