KSnip
Scissors, scissors, screen! FREE | BIT.LY/2MMADRT
Almost all Linux users want to populate their desktops with small, handy accessories that make everyday life easier. Windows’ standard snipping tool accomplishes the builtin system screenshot-taking feature, usually bound to the Printscreen button. Although you can slightly customise its behaviour, all other useful features, such as drawing arrows over a grabbed picture, are only available in snipping tools or third-party commercial apps. Remarkably, Linux desktops still lack out-of-the-box snipping tools.
KSnip is a clone of the Windows snipping tool — a compact floating always-on-top window, which lets you grab a custom part of the screen and quickly emphasise something in it. You can draw lines, rectangles, ellipses or use the highlighter in a non-destructive way: everything is superimposed over the image and you can always move or delete any drawn object. There is no arrow tool right now, but you can draw straight lines by holding down Shift and using the Pen tool. The Ksnip settings window hides default drawing colours and also the very useful Imgur uploader (authentication is supported).
Ksnip is currently in active development. When we first came across this, it didn’t have rectangle or ellipse drawing tools, so you can bet that there’s more still to come.
For some reason, the code sticks to the legacy Qt 4.8 version, however, and also needs GCC 4.8 for successful compilation. The KSnip developer expressed hope for porting his app to Qt 5 in the mid term, but it will require significant code refactoring.