OpenBoard
I have quietly been waiting for Open-Sankoré to update and support OS X Yosemite and/or El Capitan. OpenBoard (a fork of Open-Sankoré) works on OS X Yosemite and El Capitan, and looks pretty much identical.
Finding OpenBoard can be a little difficult, but can be downloaded here.
Interesting enough, Uniboard (the software that Open-Sankoré was based on) works in OS X El Capitan. The origin site to download it, however, does not:
Uniboard can be downloaded from Download.com
So, Uniboard and OpenBoard can both work on recent versions of OS X. My recommendation at the moment would be OpenBoard.