There are several tools that accomplish some of what JoinMe does, but none that tie all of the features together in such a compact, easy to use package. As with the other tools here, the basic version is free, but a premium offer with more features is also available.
At its core, JoinMe provides instant screen sharing and free voice conferencing access. That makes it great for collaborative projects and group meetings. That's not as big a deal when you have a traditional classroom course, but when you have students scattered across multiple states (or continents) working on a project together, this allows closer contact than email, discussion posts, or IMs. Yes, you can use Google+ Hangouts to accomplish that, but JoinMe has an additional feature that trumps them. JoinMe provides the option to give one or more of your meeting participants control over your PC. That makes it a good tool for tutoring, real time editing, and tech support.
Only the host needs to download any software, a small client stub. Clients connect by going to the JoinMe website and entering a random 9 digit code that the host provides them by email or text. The Host can also create a dynamic link that allows clients to directly connect without going through the website. This one is definitely a keeper.
Alternatives to Powerpoint are proliferating these days, and some of the best are cloud-based entities. One of the more interesting options is Projeqt, which promotes itself as allowing dynamic presentations for a "realtime" world, and is designed to for "creative" storytelling presentations. Projeqt has three key features that make it worthy of consideration and separate it from competitors like Prezi (see below).
This the most visible difference from Powerpoint - Projeqt allows users to create a layered presentation. The top layer is the first level of the presentation, and navigates like a Powerpoint clone. However, you can make any slide into a stack that you can drive down into for more detail. Not only does this allow you to make comprehensive presentations that include galleries of supporting information that you can call (or ignore) as needed, but each presentation can also act as a portfolio, with each stack acting as a mini-presentation of its own.
The second key feature Projeqt offers is the ability to embed live data from other sites into your presentation. While importing content from websites and applications is old hat by now, this is a whole different animal. Projeqt lets you embed streams of content from twitter, RSS, Vimeo, Google Maps, etc... and constantly updates those streams as you use the presentation. If you embed Google Maps, for example, you get the full functionality without ever leaving your presentation. When you embed a twitter search, all items for the hashtag are constantly updated. The opportunities for presentations covering rapidly changing events are pretty interesting, and it keeps the content from ever becoming stale. The downside is that you have to find other ways to add content that needs to be static.
Projeqt's final feature is cross-platform compatibility for phones, tablets, laptops. The dynamic player changes the way presentations appear on each device so that you get appropriate content views and navigation regardless of how you access the presentation.
On first glance, Daytum seems kind of weird. It's basically a tool that allows users to collect categorize, and communicate data. This thing is a marketer's or data miner's dream because it not only allows you to enter any data you want, and categorize it, but to make custom displays of that data so that you can present it visually or perform a variety of sorts and statistical functions. I'm not sure about how my students would use this, but it would be great for data heavy disciplines like sociology, political science, hard sciences, and business. This is the type of thing that nonprofits should be using when they develop their annual reports.
Prezi is the last of the tools that caught my eye. Like Projeqt, it is presentation software with cloud storage I was already a bit familiar with Prezi since many of my students use it to create fantastic presentations for my World Civilizations I & II courses. What makes Prezi different than other presentation packages is that all work takes place on a giant canvas that users place their information on. Content can go anywhere on the canvas, and it zoomed in on for display (giving the feeling of interactivity). Users create a path to move through the content in creative, sometimes mind-boggling ways. Individual slides can be of various shapes, and creators can make the frame for the slide invisible, add images, text, video, or audio. Multimedia content can be uploaded from a computer or embedded from sites like Youtube. One of the coolest features is that existing Powerpoint slides can be uploaded and converted to develop fresh presentations of existing content.
The presentation path is easy to change, so that a single Prezi can contain hidden information. This allows a single presentation to be easily adapted for audiences or circumstance. One example of this is that if you know that your presentation will be given in an area without Internet access, you can add static versions of online content your presentation uses and edit the path to include it when offline. You could also use this feature to create an executive summary version of the presentation within the more comprehensive version.