Modern teachers who are looking for new ways to connect with colleagues, communicate knowledge, create courses, and engage students can find everything they need online. There are many different websites that provide free tools and resources for the 21st century teacher. Here are ten sites to explore in your spare time.

We The Teachers - We The Teachers (WTT) is a social site for teachers who want to network, share lesson plans, and discuss education-related topics online. Site members can try out WTT alone or join groups of like-minded teachers.

LearnCentral - LearnCentral is a social learning network for educators who want to network with colleagues and collaborate on a global level. Teachers who sign up for a free membership are given their own virtual meeting room with two-way VoIP, an interactive whiteboard, and application sharing capacity.

Edutagger - Edutagger is a new social bookmarking site for K-12 teachers. It works a lot like Delicious and other bookmarking sites but focuses exclusively on education-related content.

Engrade - Engrade is the perfect online tool for teachers who want to create a secure, online classroom community. It can be used to track and store assignments, grades, class attendance, and much more.

Edmodo - This free social platform is an excellent resource for teachers who want to be able to share assignments, files, and other content with their students over the web. Edmodo can also be used to create an online group or class.

TeachStreet - This site provides an array of tools to help educators grow their teaching business. Teachers can TeachStreet to network with other teachers, list events, promote classes, and collect online payments from students.

Eduslide - Eduslide makes it easy for teachers to create and deliver their own presentations, slide shows, and courses online. Teachers can make Eduslide content publicly available to anyone who wants to see it or restrict access to a specific group of people.

TeacherTube - TeacherTube is an online community for teachers who want to share instructional videos. Videos can be aimed at students or other educators.

Teacher Lingo - This online community is for blogging teachers who want to share their content and ideas with other educators. The site has a blog feed, message board, and a space to share lesson plans.

Vyew - Vyew is a collaborative tool for teachers who want to host webinars, presentations, and meetings online. The site can also be used to create and upload course content for real-time instruction. The free version of Vyew allows up to ten real-time participants.

Guest post from education writer Karen Schweitzer. Karen is the About.com Guide to Business School. She also writes about online college classes for OnlineClasses.org.

The open source movement has made many different educational programs freely available to schools, teachers, and students. Many of these software programs are designed to work across multiple platforms and include directions for use and installation. Here are 10 educational software products that can be downloaded or used online for free.

ATutor - Similar to Moodle, ATutor is an open source web-based learning content management system (LCMS/LMS). It provides students with a social learning network and allows teachers to conduct courses online.

SugarLabs - SugarLabs offers an award-winning learning platform for children. The free platform allows children to collaborate, communicate, write, and make music together in a safe environment. SugarLabs’ software is available in 25 languages and is used by more than one million students around the world.

MediaWiki - Originally written for use on Wikipedia, this free wiki software works well for classroom wikis. The software includes full installation instructions and allows users to restrict anonymous editing, reading, and account registration.

Elgg - This open source program can be used to create social networks for education and other school-related projects. Elgg provides everything needed to build a site or application from the ground up and offers frequently updated patches, plugins, and themes.

Anki - Anki is a free and open source spaced repetition system (SRS) that can be used to create smart flashcards and scheduled study periods. The software works online, on computers, on cell phones, and with several different portable devices.

Pauker - Pauker is an open source learning application that is available in multiple languages, including English, Esperanto, Dutch, German, French, Polish, Spanish, Slovak, and Vietnamese. The application is flashcard-based and meant to help people memorize everything from abbreviations to state capitals.

StarDict - StarDict is a free international dictionary and translator that works across multiple platforms. You can use the online version or download the StarDict software to your computer for free.

Tux Paint - Designed for children age three and up, this award-winning open source drawing program offers a friendly user interface and a wide range of drawing tools. Children can get creative with a paint brush, line tools, shape tools, text and label tools, rubber stamps, and many other easy-to-use special effects.

VoiceThread - VoiceThread is a web-based application that allows multiple people to collaborate on a slide show presentation. Users can comment together on images, documents, and videos. Several versions of VoiceThread are available; the free version allows unlimited voice threads and 2GB of storage.

Google Wave - Google Wave is a new Google tool that can be used to communicate and collaborate online in real-time. The software isn’t freely available yet, but you can request a special invitation to try out Google Wave with students or colleagues.

Guest post from education writer Karen Schweitzer. Karen is the About.com Guide to Business School. She also writes about online degree programs for OnlineDegreePrograms.org.