IBM sametime can be used as a stand-alone desktop client, web browser client, embedded client within Lotus Notes so it's very versatile.
Many many plug-ins and mods have been produced for sametime which really add to the extensibility given is how it has been built on the Eclipse Java platform. For example you can easily add time zone support, fancy emoticon packs, integration with other tools, fancy alerting features, automation features, the list goes on and it's very impressive.
Additionally the sametime protocol can be used out with IBM's clients. So for example one can configure and log on to the same time community using generic messaging client like Pidgin.
Different community icons are automatically shown for contacts from different communities and favourite contacts can be added into a separate queue for ease of access.
One can share screen with colleagues and schedule web conference meetings also using platform.
File sharing is also implemented very well and works extremely quickly. In fact this is my preferred method of transferring large files quickly and easily peer-to-peer.
Lastly like Skype one can use same time to voice chat over VoIP as well as the usual messaging.
Sometimes the mods or plug-ins can cause same time to run very slowly and IBM have made it difficult to use the same time protocol with third-party generic clients like Pidgin.
Also using the sametime embedded notes version dramatically increases memory usage on any machine and therefore is not recommended for low-end machines.
Do not add too many contacts to same time because it can slow down the usage of the client especially when there are issues with synchronisation with the server. In any case, any user can be searched for on the server live every time you want open a chat.
Mainly sametime can be used very well for the following activities Instant messaging, collaboration, screen sharing, web conferencing, voice VoIP calling, screenshot grabbing.
Any activity that happens on a local machine is automatically backed up to the community server so there is no loss of contacts should a machine fail as once you log back in with a fresh reinstall it downloads all your contacts again.
The modelling and plug-in library for sametime is very impressive and one can really configure this messaging client to one's exact specification which is very rare with other messaging clients.