This unique app combines a calendar/scheduler with a text editor. It's great for keeping a diary, tracking your thoughts, or leaving yourself notes about upcoming events and tasks. Operating System: Windows, Linux
1. Makagiga
Like RedNotebook, Makagiga includes a to-do list, calendar, and text editor, but it also adds a feed reader and a sticky-note widget. You can also import and export documents from other applications. Operating System: Windows, Linux
2. ThinkingRock
This app helps you put into practice the "Getting Things Done" methodology featured in books by David Allen. Different screens help you collect your thoughts, process thoughts, then organize, review, and do. Operating System: Windows, Linux
3. Task Coach
Most to-do list programs lack the ability to break a task into smaller components, but not this one. It's also portable so that you can take it with you on a smartphone, iPod, or other device. Operating System: Windows, Linux, OS X, and others.
4. eHour
While the other projects in this category can help a single person become more efficient, eHour can help an entire office staff track their time. Designed for consultants, freelancers, lawyers, and other small businesses that charge by the hour, eHour can track multiple employees, multiple clients, and multiple projects. Operating System: Windows, Linux, OS X.
5. Stellarium
If you've always wanted to learn more about astronomy, Stellarium can help. It allows you to view the night skies from any point on earth at any time. It's so accurate, it's even used to power many planetariums. Operating System: Windows, Linux, OS X.
6. Celestia
Celestia takes the capabilities of Stellarium one step further. Instead of just viewing the night sky from earth, you can also fly through the virtual heavens to view the sky as seen from Mars, Jupiter, or any other point in the known galaxy. Operating System: Windows, Linux, OS X.
7. Gramps
Gramps (short for "Genealogical Research and Analysis Management Programming System") makes it easy to get started on the popular hobby of genealogy. It boasts a very active user community and nearly 1,000 pages of online help. Operating System: Linux, Windows
8. GenealogyJ
This Java-based genealogy app lets you view family information as a family tree, in a table, on a timeline, or by geographic location. It's appropriate both for people looking for a hobby and more serious historians. Operating System: OS Independent
For those interested in interior decorating as a hobby, Sweet Home 3D lets you create a 2D floorplan and then see what your room will look like in 3D. If you don't want to download the software, you can also use the app online and even save your data in the cloud for free. Operating System: Windows, Linux, OS X.
10. LenMus
Whether you're an accomplished musician or just a beginner, LenMus can help you improve your musical skills. It covers the fundamentals of music theory and site reading, with plenty of exercises for practice. Operating System: Windows, Linux, OS X.
11. GNU Solfege
Even if you weren't born with perfect pitch, you can improve your "ear" for music. This app offers ear training exercises that teach you to identify intervals, sing intervals, identify rhythm patterns, sing scales, sing chords, and learn harmonic progressions. Operating System: Windows, Linux, OS X.
12. Numismatic
Looking for a hobby with an impressive-sounding name? Become a numismatist, otherwise known as a coin collector. This app can help you track your collection in a MySQL database. Operating System: OS Independent.
13. JDiveLog
Want to try a more adventurous hobby? How about Scuba? JDiveLog is a digital logbook for scuba divers with a huge list of features. Operating System: Windows, Linux, OS X.
14. jVLT
Short for "Java Vocabulary Learning Tool," jVLT combines flashcard, dictionary, and quizzing capabilities in a single app. You can make up your own vocab list or use one of the built-in libraries which include German-French, Thai-English, French-English, practical Chinese, and several other lists. Operating System: Windows, Linux, OS X.
15. Zkanji
If you've always wanted to learn Japanese, Zkanji can help. In essence, it's a very elaborate Japanese-English dictionary, with a number of special tools to help you read, write, and recognize kanji symbols. Operating System: Windows.
16. ZWDisplay
Practicing Chinese on your own can be very difficult, but ZWDisplay makes it easier by pronouncing Chinese words for you. You simply input a Chinese word, and the app pronounces it for you and shows you the pronunciation in pinyin. Operating System: Linux.
17. FBReader
Reading is more convenient when you can take ebooks with you wherever you go. This app lets you use a netbook, laptop, or other Windows- or Linux-based devices as an ebook reader. Operating System: Windows, Linux