Let it be known that the “OpenType Collection” (OTC) format was born on 09/21/2011 at Pho Minh Restaurant in Cupertino, California. Present from Adobe were the following: David Lemon, Ken Lunde, Sairus Patel, and Read Roberts. Present from Apple were Antonio Cavedoni, Julio Gonzalez, Yasuo Kida, Peter Lofting, and Tony Tseung. — Adobe & Apple
The above declaration paved the way for supporting (CFF-based) OpenType Collections in Apple’s OS X (beginning from Version 10.8) and in Adobe’s applications (beginning from CS6).
As far as I am aware, the Adobe-branded Source Han Sans and the Google-branded Noto Sans CJK fonts represent the very first deployment of OpenType Collections.
TrueType Collections, meaning those with TrueType glyphs, have been supported in OS X and Windows for a long time, probably for over 15 years. At this point, support for TrueType Collections is effectively ubiquitous. OpenType Collections are a different matter, because they are not supported in any flavor of Windows OS, and the only work-around is to use an Adobe application, CS6 or greater, and install the OpenType Collection file into that application’s private font folder. I have my fingers—and toes—crossed that Microsoft will eventually support OpenType Collections in a future version of Windows.
What makes OpenType Collections very compelling for Pan-CJK fonts—besides offering a convenient work-around for the lack of ‘locl‘ (Localized Forms) GSUB feature and language-tagging support in most applications—is that they can nearly decimate the file size when compared to the component OTFs.
Using the current (Version 1.001) Source Han Sans fonts as an example, the combined size of the four language-specific OTFs for the ExtraLight weight comes in at 60.5MB (60612376 bytes), but the single OTC for the ExtraLight weight is a quarter of that size at 16.5MB (16413189 bytes). Of course, the significant reduction in file size is mainly due to the sharing of the ‘CFF’ table. Taking this further, the combined size of all 28 language-specific OTFs, covering all four languages and all seven weights, is a mighty 460MB (460123852 bytes), but the Super OTC is again about a quarter of that size at a still-impressive 114MB (113886690 bytes).
Lastly, I would like to remind readers that we developed two scripts for assembling and disassembling OpenType Collections, to include their TrueType versions, that were added to AFDKO a little over a year ago. In other words, developing and managing OpenType Collections has become simpler.