I usually use GIMP (the "GNU Image Manipulation Program") for editing photos, changing colors, resizing photos, applying significant effects and more. It is a free software alternative to Adobe Photoshop. It is also quite popular with graphics artists and webmasters who wants to edit digital images. GIMP is not just a Linux specific program. It works on all leading operating systems, i.e., Mac OS X, MS-Windows and Unix variants. However, like many other powerful open source software, GIMP can be difficult to master. There are many options and plugins. So if, you are looking to learn or master the GIMP program, give The Book of GIMP a try.
Goldendict is a cross-platform (Linux/Unix/MS-Windows/Apple OS X) and dictionary lookup app written in QT. This application support of multiple dictionary file formats. The program can search Wikipedia, Wiktionary, or any other MediaWiki based sites to perform lookups. You can listen to pronunciations for any word or setup text to speech to read out pronunciations. The dictionary also provides word stemming and spelling suggestions. You can also use this program to find out translations of words and phrases for different languages. A commercial mobile version is also available for Android based devices.
Personally, I consider programming as a fundamental right. The programming will teach children problem solving and reasoning skills. So, if you have gifted kid or nephew who is about to turn 10 or 11, gift him Python for kids book. The book introduces kids to the basic concepts of Python programming. The kids require no previous programming experience. However, must understand basic math concepts.
Geany is a great and light weight cross-platform integrated development environment for Linux and Unix based systems. It supports C, C++, Java, PHP, Python and 50+ other programming languages. Geany is known to run under Linux, FreeBSD, NetBSD, OpenBSD, MacOS X, AIX v5.3, Solaris Express and Windows. Geany more closely resembles programming editors available for Microsoft Windows such as Notepad++. So if, you are switching from MS-Windows to Ubuntu/Debian/Fedora/Mint or BSD/OS X/Unix like platform try geany IDE.
Shutter is a free, open-source, and feature-rich screenshot tool for GNU/Linux distributions. I use this tool frequently when I am creating resources for this site or for our youtube channel and it has not yet let me down.