Guitar is described as 'Git GUI Client' and is an app in the Development category. There are more than 25 alternatives to Guitar for a variety of platforms, including Mac, Windows, Linux, Android and Android Tablet. The best alternative is SmartGit. It's not free, so if you're looking for a free alternative, you could try GitKraken or GitAhead. Other great apps like Guitar are Sourcetree (Free), GitHub Desktop (Free, Open Source), Fork (Paid) and TortoiseGit (Free, Open Source).
SmartGit is a front-end for the distributed version control system Git and runs on Windows, Mac OS X and Linux. SmartGit is intended for developers who prefer a graphical user interface over a command line client, to be even more productive with Git.
TortoiseGit is a Windows Shell Interface to Git and based on TortoiseSVN. It's open source and can fully be build with freely available software. Since it's not an integration for a specific IDE like...
Git Extensions is a standalone UI tool for managing git repositories. It also integrates with Windows Explorer and Microsoft Visual Studio (2010/2012/2013/2015/2017). Linux is supported by 2.51 version with some issues.
Tower is a native desktop Git client for both macOS and Windows. The app gives developers, designers, and non-technical people easy access to the full power of Git with features such as Pull Requests, Interactive Rebase, Image Diffing, Quick Actions, Undo and much more.