Ahh, another microsoft semi lock-in as for sharepoint....at least that's the classic goal
As noted below, doc checkin with MS office & wine work pretty well.
Depends on what one really needs to do with it. Think of it as a google drive you can share with others, or likely more comparable to a less focused but reasonably capable project/code/document collaboration systems such as joomla or numerous others. I've seen it used for document collaboration, it's main theme is ease of use for the non techie project manager.
It can be accessed via webdav (shared drive via webtype protocols), all the way to installing MS office and code dev tools under wine or native to whatever software platform (main themes are revision control, project management, task assignment, reporting to teammembers). standard disclaimers apply, but the sharepoint name is fairly accurate. big difference between that and more popular doc/code repositories that are open standard based is the integration with MS products primarily. Others (typically freebees, some with paid versions) have significantly extended functionality.
Ironically, I worked on the review a couple years ago where MS agreed in court to share documentation on their APIs to facilitate other companies (or FOSS) to access many MS programs. MS is pretty awful in misreading/abusing standards, and my review wasn't that kind (the API docs were terrible, and RFC/protocol abuse was rampant).
I use (happy to spend the $$ and often great deals are out there) for crossover office (many wine authors pay their bills via this product set). Run MS office without any hassles, but I doubt I use it for more than the most basic (and common) deployments of anything like sharepoint.
Check over on freshmeat.net and look around for the tasks that might be sharepoint comparable. They'll give you some ideas as to what everyone really uses if the type of project/work/assignment is more intensive.
Worst case, virtualbox and a copy of windows there can satisfy the 3% of time needed to handle checkins, etc.