Earlier this month I published a review of seven free services teachers can use to create and conduct online courses. Those services are good for on-going courses that contain a series of lessons. But sometimes you might just need a quick and easy way to give a short online lesson. In those cases you might want to try out one the following free services.
Big Marker is a good option for conducting online tutoring sessions, brainstorming sessions, and other online presentations. Big Marker allows you to create your choice of a private or a public online meeting room. If you make your room public anyone can join. If you make your room private you have to give participants a password to enter the room. Once in your Big Marker conference room you can share screens, chat via text, chat via audio, or turn on your webcam so that people can see and hear you. Your Big Marker conference room comes with a white board that you and your participants can write and draw on. As the creator of a Big Marker conference you can control who can and cannot be heard or seen in the live audio and video chats.
Zipcast is a new service from Slideshare for conducting online presentations. Using Zipcast you can share your slides, talk to your audience, respond to your audience, and have your audience interact with each other in realtime on one page. The best part is you can do all of this without having to download anything. Using the free version of Zipcast your presentation can be private or public (a small ad is inserted at the bottom of your presentation). The premium version of Zipcast removes ads and allows you to password protect your presentation.
Scribblar is a free, simple service designed for creative, real-time collaboration. Using Scribblar, users can collaborate on the creation and editing of images and drawings. Scribblar also supports the use of mathematics functions in your whiteboard. If you have an image you can upload it to your whiteboard where you and others can edit it or comment on it. The commenting can take place directly on the whiteboard or in one of two side bar chat options. Users can chat in text or in voice. Using the voice chat feature and the mathematics function could make Scribblar a good tool for conducting mathematics lessons online.
Join.me is a free service offered by Log Me In. Join.me allows Mac and Windows users to quickly share their screens with each other and work together. To use Join.me you do need to download the Join.me client. Once you’ve downloaded the client you can start sharing your screen with anyone you like. Just give your nine digit access number to your collaborators to give them access to your screen and to converse with you. Use Join.me to share a slide presentation and chat or share scientific calculator on your screen and explain to students how to solve an equation. 
