I can talk from personal experience that usually one of the two problems appear when developing cross-platform products: 1. The documentation states that the A

I can talk from personal experience that usually one of the two problems appear when developing cross-platform products: 1. The documentation states that the API is 99% the same and should be sufficient to write most applications except the most advanced ones. And then you hit that one difference which is required for feature parity between platforms which requires either a small hack or a massive workaround which will have to be supported indefinitely. 2. Even if the APIs are the same, the performance characteristics of the systems are different because some of those systems might not be meant to satisfy the same use cases as others and different workarounds are required for cross-platform support. Dropbox desktop application might look simple from the outside, but it must contain some advanced features that its user base might require: directory exclusion from syncing, real-time file sync progress monitoring, displaying the UI status of the synchronization, real-time file change monitoring (as opposed to scanning the directory periodically for modification dates or content changes in the worst case) and many others I couldn't think of right now. So, basically, you can almost always find some open-source alternative for your needs but it will probably only be tested on one platform and will probably contain only a subset of features. I recently had a hard time finding a good enough implementation for Google Drive for Ubuntu.