A live CD Linux distribution can offer a full-fledged computing environment on a CD or DVD, but if you have access to a Windows-based machine, a removable storage device with Windows portable applications might be a better option. Luckily, using a Windows machine doesn't mean you can't use open source software. Many of the most popular portable applications are, in fact, open source: applications like OpenOffice.org, Thunderbird, Firefox, and Gaim. Let's take a look at some of the lesser-known and most useful portable applications you can put on your USB flash drive or mobile hard disk.

FullSync

FullSync is a Java-based utility that allows you to synchronize and back up directories on Windows. Actually, FullSync is not a portable application, but it can come in handy if you need to keep the applications on your computer and a removable storage device in sync.

For example, if you use Portable Firefox and Thunderbird, you might want to keep bookmarks, settings, email, and other stuff on your mobile hard disk in sync with their siblings on your computer. To do this, you create a FullSync job that synchronizes data in your Firefox and Thunderbird user profile with the profile on the mobile hard disk.

Torpark

If you plan to access the Web from public computers or from work, security and privacy should be your primary concerns. While Firefox allows you to remove all the private data saved on the disk, it does nothing to secure the Internet connection itself.

For security and anonymity, you can use Torpark, a combination of Portable Firefox and Tor. Tor uses a distributed network of servers called onion routers to create a secure and anonymous connection to the Internet. Torpark comes with integrated and preconfigured Tor software -- just launch the application and it takes care of the rest.

Torpark is rather slow, however, so if you want to use an application that demands a low-latency connection, such as the OpenWengo VoIP application (which I'll talk about in a moment), then you would be better off using it with Portable Firefox.

KeePass and Password Safe

Want to keep passwords and login data on a USB key? KeePass allows you to store all your passwords in an encrypted database. The database itself can be encrypted using either Advanced Encryption Standard (AES) or the Twofish algorithms, which are virtually impossible to break. You can use KeePass to group and sort multiple passwords as well as add new password groups and subgroups.

If you don't need all the bells and whistles of KeePass, you might want to opt for PasswordSafe, a simple utility that allows you to store user names and passwords in an encrypted database. The clever bit is that when you select a record, Password Safe copies the password from it into the Clipboard (you can change this behavior in the program's settings). When you close Password Safe, it clears the Clipboard, so no passwords are left behind.

TrueCrypt

One of the most effective ways to keep your documents and sensitive data on a USB key secure is to store them in an encrypted area of the device. TrueCrypt allows you to do this.

To install TrueCrypt on your USB key or mobile hard disk, launch TrueCrypt on your computer and choose Tools -> Traveller Disk Setup. Once TrueCrypt is installed, you can create an encrypted volume based on either a file or a partition. A friendly wizard guides you through the process of creating an encrypted volume and provides explanations of TrueCrypt's features. Mount the volume using TrueCrypt, and you can work with it as with a conventional disk drive.

NeoMem

NeoMem is a nifty little free-form database application that allows you to store virtually any type of information, including passwords, serial numbers, links, contact lists, notes, and anything else you can think of.

NeoMem allows you to define different classes, such as hardware, password, or bank account. Each class has its own properties, including a set of fields. For example, the bank account class would include the bank name, account number, type, notes, and so forth. You add a new record by creating a new object that belongs to a certain class. In this way, you can keep different bits of information in the same database. More importantly, NeoMem allows you to encrypt the created databases -- an essential requirement for any application that takes care of your private data.

Rainlendar

Despite its tiny size, Rainlendar is a great calendar utility that offers many useful features, such as support for whole-day and recurring events, event categories, reminders, and to-do lists. Rainlendar is not a portable application per se, but it will happily run from a USB key. Download a compressed version of Rainlendar, unzip it, and move to the USB key. If you already have Rainlendar installed on your computer, and you want to keep both calendars in sync, you have two options. You can use FullSync to copy the events.ini, todo.ini, and rainlendar.ini files to the Rainlendar folder on the USB key, or you can run the Rainlendar server, and use it to sync calendars.

Openwengo

If you are looking for a portable VoIP application, Openwengo will get you covered. Openwengo is open source software based on open standards, and it's available in two editions: as a standalone application and as a Firefox extension. The latter can be easily installed on Portable Firefox. To place calls with Openwengo, you have to create an account and purchase call credits. Openwengo allows you to call landline phones at rates comparable to those of Skype.

Damn Small Linux

If you want to run a full-fledged Linux desktop from your USB key, look no further than Damn Small Linux (DSL). This slim Linux distribution fits on a 128MB USB key, and it contains all the applications you are likely to need on the move.

Better yet, Damn Small Linux is available with the QEMU emulator, which allows you to run DSL from within Windows. Download the file dsl-embedded.zip from one of Damn Small Linux's mirrors, unzip the file, and launch QEMU by double-clicking on the dsl-windows.bat file. Admittedly, running DSL using QEMU is a painfully slow affair, but it does allow you to run Linux without leaving Windows and rebooting the computer.

Miscellaneous applications

Of course, these applications are just a tiny fraction of the available open source portable software. You might want to consider these portable applications as well.

• TightVNC is a great VNC server and viewer package that allows you to access and control remote computers.
• LockNote is a simple notepad with built-in encryption.
• Portable Thunderbird is a portable version of Mozilla Thunderbird, a popular open source email client.
• nPOP is a good choice if Portable Thunderbird is overkill for your email needs.
• Explore2fs is a simple tool that allows you to access Linux ext2fs partitions.
• Wackget is a Windows-based version of wget. It can help you to manage downloads.
• VLC media player can play virtually any media format.
• XAMPP Lite lets you run a full-fledged Apache/MySQL/PHP server from your removable disk.
• Miranda IM is a lightweight IM client that supports IRC, ICQ, MSN, Yahoo, AIM, and Jabber.
• Notepad++ is a text editor that offers syntax highlighting, regular expressions, and drag-and-drop functionality. It offers a tabbed interface (which allows you to quickly switch between multiple documents), multi-view mode (useful for viewing two documents side-by-side), and text zoom.

Obviously, if you want to replace your laptop with a USB key on your next trip, you won't have difficulty filling it up with useful applications. The software described here is enough to cover most of your mobile computing needs. Just make sure that the place you are heading to has a computer you can use with your USB key.

• 7-Zip 4.16 Beta：文件压缩工具，可与Windows资源管理器集成
  
• A Note 4.2.1：可在Windows桌面放置便笺，并可提供闹钟提醒功能
  
• Abakt 0.9：能够以压缩方式对文档进行备份
  
• Abiword 2.27：Windows写字板的替代程序，功能有所加强
  
• Aethera 1.21：提供日历、通讯录、任务表及提醒功能，并且内置了e-mail客户端
  
• Ant Movie Catalog 3.5：将你收藏的DVD影碟归档，并添加说明信息
  
• Ant Renamer 2.0.8：易用的文件重命名工具，并具备灵活的筛选机制
  
• Audacity 1.2.3：对音频文件进行编辑、优化并添加特效
  
• Axcrypt 1.6.1：对程序进行加密，可与Windows资源管理器集成
  
• Blender 3D 2.36：三维对象的建模、渲染
  
• Borg Calendar 1.4.2：提供桌面日历、任务列表、通讯录功能，支持多用户
  
• Cdex 1.51：将音乐CD转换为wav或者mp3格式
  
• Cinepaint 0.19：专业的图像编辑软件
  
• Clam Win 0.83：病毒扫描工具
  
• Cool Mon 1.0.1003：系统检测工具
  
• Cool Player 215：一款精简的音频播放软件
  
• Dia 0.94：绘制图表和流程图
  
• Double Type 0.2.1：设计自己的Truetype字体
  
• Egroupware 1.0.0.006：一款包含日历、新闻、联系人等模块的工作流系统
  
• Eraser 5.7：永久地删除硬盘中的数据
  
• Filezilla 2.2.12c：FTP客户端
  
• Firefox 2：Web浏览器，支持并列显示多个网页
  
• Freemind 0.8：能以直观形象的图示建立起各个概念之间的联系
  
• Gaim 1.4.0：同时支持ICQ、Aim、MSN、Yahoo的即时通信软件
  
• Ganttproject 1.11.1：项目管理软件，帮助你进行时间安排及资源分配
  
• GnuPG Add-ons：对邮件进行加密
  
• Health Monitor 2.1 Monitors：Windows状态监测工具，出现问题时可以给出警报
  
• Inkscape 0.41：向量图形设计工具，可用来绘制地图、技术图纸或公司logo
  
• JDictionary 1.8：超过140万词条的百科辞典
  
• Kee Pass 0.99b：管理你的密码
  
• Keynote 1.6.5：字处理软件和数据库的结合体，带有良好的搜索机制
  
• Media Portal 0.1.1.1：视频、DVD、音频、图片播放工具，同时支持电视和电台广播
  
• MP3 Tag Tools 1.2.008：mp3的文件ID标签编辑工具
  
• MP3 Gain 1.2.5：在不影响音质的情况下调节mp3歌曲的音量
  
• NVU 1.0：所见即所得的HTML编辑工具，带有相当专业的网页制作功能
  
• Open Office 2.0 Beta：文字处理、电子数据表、演示工具和数据库
  
• PDF-Creator 0.8.1：可被安装为打印机并将文档输出为pdf文件
  
• Poptray 3.10：在后台监控邮件账号，当有新邮件进入时对你进行提醒
  
• PW-Gen 1.4.0：为你生成64位到128位的安全密码
  
• RSS-Owl 1.1：RSS阅读器
  
• Screencopy 2.3：屏幕拷贝工具
  
• Syn Text Editor 2.1.0.46：文本编辑器，支持多种程序语言的命令语法
  
• Task SwitchXP Pro 1.1.2：扩展了Windows任务管理器的功能和外观
  
• The Gimp 2.2.4：支持图层管理、特效润饰的图像编辑软件
  
• Thunderbird 1.07：e-mail客户端，支持Imap/Pop3账户，带有垃圾邮件过滤器和虚拟文件夹
  
• True Crypt 3.1a：对文件或硬盘分区进行加密，也可以对U盘等移动存储介质进行加密
  
• True Downloader 0.82：FTP和HTTP链接的下载管理工具，可以监视剪贴板
  
• TV-Browser 1.0.1：自动更新每天的电视节目表
  
• Virtual Dub 1.5.10：视频编辑和捕获软件，支持mpeg-1和avi视频格式
  
• Virtual Win 2.1：可管理最多9个虚拟桌面，你可以用热键进行桌面切换
  
• VLC Media Player 0.8.1：媒体播放器，支持DVD、VCD、CD、mpeg和DivX等格式
  
• Web HTTrack 3.33：离线浏览器，可将Internet网页保存到本地硬盘中
  
• Winroll 2.0：点击标题栏后就可将程序窗口最小化
  
• WX Musik 0.4.1：音频播放及管理软件
  
• Xampp 1.42 ：Web服务器软件包，包含Apache、PHP和MySQL