Free/opensource application is closed to linux or other application running under linux, this statement maybe not one hundred right cause lot of application (same application) can run both linux or windows operating system take OpenOffice from Oracle as an example. Every application need to be installed to colaborate with their parent system operation except application called "portable application". A portable application (portable app) is a computer software program that is able to run independently without the need to install files to the system it is run upon. They are commonly used on a removable storage device such as a CD, USB flash drive, flash card, or floppy disk, A portable application does not leave its files or settings on the host computer (wikipedia). 

There are many portable application has been shared in internet, many website like provide many prortable application can be download and place to our pendrive/flashdisk, here you are 10 usefull free/opensource portable application most frequently used.
  1. Putty Portable: is application to remote other computer via ssh/telnel. link for download
  2. Notepad ++ Portable : is a free (as in "free speech" and also as in "free beer") source code editor and Notepad replacement that supports several languages, link for download  
  3. Command promt portable : Command Prompt Portable is a simple utility that allows you to have a custom command line setup on any Windows computer you come across. link for download 
  4. ClamWin Antivirus Portable is a Free Antivirus for Microsoft Windows. It provides a graphical user interface to the clam Anti Virus engine. link for download
  5. OpenOffice Portable : is a free word processing program similar to Microsoft Word, link for download
  6. Mozila Firefox Internet Browser :  is a fast, full-featured web browser that's easy to use, link for download 
  7. FileZilla Portable : is a fast and reliable FTP client with lots of handy features, link for download 
  8. 7zip Portable : is a file archiver (compression) utility for Windows, link for download 
  9. WinScp Portable : Portable is a free SFTP, FTP and SCP client for Windows, link for download 
  10. VLC Portable : Media player with highly portable multimedia player for various audio and video formats, link for download 
Besides 10 usefull portable application above, i have special portable application and this is my favorite, this application called stellarium which will bring planettarium to our desktop. Here the link for download and clik here for more detail about stellarium.