I would like to add my understanding of OSL 3.0.
The point is that OSL 3.0 license applies to Derivative Works.
The OSL 3.0 Approach To Derivative Works
OSL 3.0 is far simpler, with the entire copyright and copyleft bargain stated in a short § 1 that echoes the provisions of 17 USC 106 and similar copyright laws. Section 1(a) authorizes licensees to make "copies [of the Original Work], either alone or as part of a collective work", and § 1(b) authorizes licensees "to translate, adapt, alter, transform, modify, or arrange the Original Work, thereby creating derivative works ("Derivative Works") based upon the Original Work."
Then § 1(c) requires any copies of that Original Work and any Derivative Works that are distributed to be distributed under OSL 3.0 and, for those works, the Licensor promises to provide Source Code [§ 3]. In this way, the OSL 3.0 license remains with the work and all its subsequent versions, and that software always remains open source. That's reciprocity.
The definition of Derivative Works in § 1(b) is particularly important. For one thing, that defined term includes no reference whatsoever to linking or to any other technical manner of making programs interoperate. The verbs used in § 1(b) ["translate, adapt, alter, transform, modify, or arrange"] reflect the kinds of activities that we generally do to create derivative literary or other expressive works, and those things—not functional linking—create Derivative Works as defined in this license. As a result, linking an unchanged Original Work with another independently-written work does not, absent more, create a Derivative Work subject to § 1(b); such an act is merely the incorporation of a copy of that Original Work into a collective work, authorized by § 1(a).
Source Code Disclosure
Only the Source Code of the Original Work or the Source Code of a modified (altered, etc.) Derivative Work must be disclosed. [§§ 1(c), 3] The GPLv2 and GPLv3 ambiguities about linking are gone from OSL 3.0. The avoidance of technical terms of art such as "linking" and a definition of "Derivative Works" that relies on well-understood copyright verbs, are some of the reasons why OSL 3.0 imposes a less-burdensome reciprocity requirement than GPL.
· If linking (by whatever technical means) can be accomplished by making and using unmodified copies of the Original Work, then 1(a) and 1(c) permit that; only the Source Code of the Original Work must be disclosed.
· Otherwise, if modifications (or alterations, etc.) to the Original Work create a Derivative Work, then 1(b) and 1(c) permit that; only the Source Code of the modified (or altered, etc.) Derivative Work must be disclosed.
· As for independent works (in the copyright sense), or the independent components of collective works, the OSL 3.0 grant of copyright license in § 1 does not affect those works at all or place any source code requirements upon them. That independent source code need not be disclosed. In this respect, OSL 3.0 is more like LGPL than GPL in its effect, although it accomplishes that with far fewer words and far less uncertainty.
I made the most interesting part of the text in bold style.
OroCRM is a CRM system built with extensibility in mind.
There's no need to modify it's source code in order to change the way it works.
In other words there's no need to create a Derivative Work from the Original Work.
So according to the license you are free to build your solution on top of OroCRM (if you're not going to modify its code) and provide access to it via SaaS without a need to make your solution Open Source.