Pixelapse

Lately, we've been using Invision to share designs amongst the team, gather feedback and quickly prototype user flows. It's been working quite well.

That being said, we're also open to new tools - such as Pixelapse, a similar collaborative workspace that was recently acquired by Dropbox. I love the sync'ing of files, Git repository style version'ing and revisions and overall presentation. On the whole, I don't think it looks markedly better than InVision but it looks interesting enough to check out.