There are a sufficient number of clients for different operating systems.
You can see them on this link - https://git-scm.com/downloads/guis.
There is a standard client on Ubuntu - gitk. But I didn't like it because it doesn't allow me to look at the entire repository. Only within one branch.
The following client - gitg - seemed to me quite good (look at the bellow picture).
You can test it. Install it on your unix system:
$ sudo apt-get install gitg
That's all. Go to the git repository, run next command and enjoy :)
$ gitg