Photo credit: Jan Spurny

1. Twiddla: Free web-based whiteboarding tool for co-browsing and audio conferencing
2. Photophlow: Share your Flickr photos in real-time while chatting with people
3. Wikisend: Share any file up to 100MB and let it stay online for up to 90 days
4. The Awesome Highlighter: Highlight any part of a page and share it with other people

1. Twiddla
   
   Twiddla is a free web-based whiteboarding tool, that you can use to collaborate with other people. With a free registration, you can create an online whiteboarding session in seconds, where you can co-browse, annotate, draw, share pictures, type, and also have voice conferences with everyone. To invite people, you can whether type their email in the invitation box, or share the room's URL. Free to use.
   http://www.twiddla.com/





2. Photophlow
   
   Photophlow is a free service that anyone can use to share Flickr photos in real-time. After you have been accepted in the beta program, you can create a room where you can invite people to chat with you, as well as sharing Flickr photos: you can search in your library or in the entire archive by entering tags or username and, when you click on a picture, a bigger version will show show for other room's participants to see. Free to use.
   http://www.photophlow.com/





3. Wikisend
   
   Wikisend is a free file sharing website that requires no registration. You just have to browse for your file, up to 100MB, give it a name and a description, set a lifetime (up to 90 days) and click upload. You will be given the file ID, that can be used to download a file from the site interface, and the sharing link that people can use without getting onto the site before. You can also set a password to protect your files. Free.
   http://wikisend.com/





4. The Awesome Highlighter
   
   The Awesome Highlighter is a free tool that you can use to highlight text on a page. From the main window, after you paste the URL you want to highlight text on, you will be brought to a page where you can highlight text by simply selecting it with your mouse. When done, you just have to click a button and you will be given a URL to share with people, so that they can see what you highlighted. Free to use.
   http://www.awesomehighlighter.com/