I would go with IRC for meetings, there exists pretty good bots to manage the meetings. Github private or public repositories for source control, bug tracker and wiki. Skype for fast one on one discussions. FTP server for sharing documents and other files.

At work we use Bitbucket, HipChat, Harvest and Basecamp, (HipChat and Basecamp is primarily for collaboration with another company)

We use the following.

(1) IRC for mostly-immediate-mode conversations and format meetings
(2) email for non-time-sensitive and formal conversations
(3) mumble, skype, and google for voice/video chats
(4) VCS for code and assets (officially we use bzr, except for certain teams who work with git upstreams)
(5) google docs for sharing documents (google docs needs a lot of work to become scalable)
(6) various third-party software for planning (kanban boards, etc)
(7) various wikis for, I dunno, stuff that no one can ever find and rarely gets updated but is quick to write so you can say "I put it on the wiki"

Pretty much all that technology is client-agnostic (except mumble and skype) and it's all freely available.

1). For real-time quick chatting, GTalk.
2). For real-time team chatting/video, G+ hangouts.
3). For non real-time, email.
4). For source sharing, BitBucket git repo.
5). For filesharing, dropbox.
6). For encrypting files for sharing, Truecrypt (Always assume that Dropbox is like leaving a file on an open share!!)
7). For wiki and docs, BitBucket provides wikis with a repo.

I'm a big fan of Zoho for project management if you've got a lot of teams operating remotely. It nicely hooks into Google mail and sets up calendar appointments and tasks as reminders.

Its also super cheap

Skype, email and a secure content management program such as a locked down Wordpress site.

It's the system that is so important, not the software IMHO. We make changes every month.