Eidetic

Eidetic is a tiny app that puts an icon in your menu bar. Right-click the icon to take screenshots with ease. Left-click the icon to display a menu which lets you quickly change the capture mode of your screenshot and access a settings panel. Here you can fine tune Eidetic’s behavior to your preferences, like switching the left and right clicking action. Also Eidetic offers a widget for your Notification Center, this is extremely helpful for creating screenshots of widgets in general. Eidetic is fully compatible with Yosemite and El Capitan, it's interface even adapts to your menu bar color.