Do you mean
For the first, good IDEs should have that functionality (e.g. IntelliJ) with some visual help.
For the second, that's not really the it's supposed to be used. You might want to ask yourself what you're using the branches for if you don't want to merge the full one. Usually it's one coherent feature, so merging everything is the only thing that makes sense (well, except for merging nothing).