[dspillett]

There are: for quite a famous example see Monotype's Arial which is effectively free for Windows/Office users and is mostly indistinguishable from Helvetica by people who are not typography experts.

Most free clones are not as good in various ways, and good clones that are charged for probably get earn their creators a letter from a foundry's legal team that makes them decide that the cost (time and money) of defending their position (even though they should eventually win) is not worth it.