I think it's fair to say that there are products that genuinely compete with Adobe Acrobat. These products don't necessarily include every single feature that Adobe Acrobat Standard or Adobe Acrobat Professional include, but they do include the vast majority of features that most people need.
The top 3 that I've used in the past are:
These three products primarily compete with Adobe Acrobat Standard. For example, they don't include many of the prepress related features found in Acrobat Professional. But since these Acrobat alternatives don't have Standard and Pro editions, there are some features, such as redaction, that can be found in the Acrobat alternatives, but not in Acrobat Standard.
There are of course a lot more products that could be considered as Acrobat alternatives, but that depends entirely on what PDF related features you require.