I currently use 2 git apps for those (gitk for browsing, git-cola for committing) ...
I use the standard tools included with git: 'gitk' and 'git gui' and they can launch each other, so even though they are two apps, they work very well together - feeling like one tool, but with multiple "views". Not to mention that they have features (command line parameters, etc) that most other GUI frontend's simply don't have (and probably never knew existed) - making them even more useful. I've tried more GUI frontends than I care to remember, and ALL of them are bloated, too limited, too memory hungry, too slow or something similar. The standard GUI tools might not look the prettiest, but they simply work the best and get the job done fast - and are available on all platforms. Oh, and for about 80% of my git usage, I use the command line directly. Again the benefit is the same syntax on all platforms, so no need to relearn tools when I hop between platforms.
Either way, this is not to discourage the author of SimpleGit. New tools are always welcome, but I do recommend you read the man pages on gitk and 'git gui' to see what the standard tools already can do - then implement those features, AND try and improve on them (more features). We don't need more "simple" (read very basic and limited) GUI tools - git is already simple to use as-is.