Yasu is a free utility that gives you a very simple interface for running system-level maintenance tasks. It is not a feature-filled system-optimization app, but rather a one-stop shop for executing Unix shell scripts that you would otherwise have to run manually through Terminal (or through some other maintenance app).
The interface is a bare-bones window with check boxes for 24 different tasks, everything from cache- and log-clearing to the Mac's "cron" scripts (which are otherwise executed automatically daily, weekly, and monthly). Yasu--which stands for Yet Another System Utility--recognizes that many system utilities offer an often bewildering abundance of tweaks and settings, so Yasu (originally designed for sysadmins) sticks to the basics. Yasu executes its tasks in the background, and a drop-down menu lets you choose whether to restart or shutdown after completion.
If you're looking for more-extensive tweaking capabilities, Yasu isn't for you. But if you want a basic, worry-free interface for troubleshooting problems and keeping your Mac healthy, this app is a great option and a good first line of defense against system weirdness.