LookUp is described as 'easy to use English dictionary app with beautiful Word of the Day illustrations and an award winning design to lookup all you want to know about about a word in a single search' and is an app in the Education & Reference category. There are more than 100 alternatives to LookUp for a variety of platforms, including Online / Web-based, Windows, Android, iPhone and Linux. The best alternative is GoldenDict, which is both free and Open Source. Other great apps like LookUp are Wiktionary (Free, Open Source), QuestSoft QTranslate (Free), Linguee (Free) and Tatoeba (Free, Open Source).
GoldenDict is an open-source dictionary program for PC computers that gives translations of words and phrases for different languages. It allows use of several popular dictionary file formats simultaneously.
QTranslate is a free translator for Windows. With this small utility, you simply select the text you want to translate and then press hot key (Ctrl+Q to show translation in the popup window or Double Ctrl click to show the translation in the main window).
At its core, Tatoeba is a large database of example sentences translated into several languages. Search example sentences translated into many languages. Add and translate your own sentences. It's collaborative, open, free, and even addictive.
dict.cc is not only an online dictionary translating from English and German to 21 languages. Its an attempt to create a platform where users from all over the world can share their knowledge in the field of translations.