OS X: Browsing Instagram on the web works well enough, but it's a fairly minimal experience and you can't post photos through your browser. Now with the newly updated desktop Instagram client Flume 2.0, you can. Flume offers a glossy, tasteful interface to easily browse your feed on your desktop, interact with your friends' photos, follow your notifications, send direct messages and, yes, even upload your pics.
There is a possible catch, though: Last year Instagram announced that they were no longer going to allow third-party applications access the Instagram feed. Developers had a deadline of 1 June 2016 to make the cut, and it seems like Flume is safe for now — it works! — but it's not clear if Flume will work indefinitely. It's free though, so no harm in trying it out.
Flume [App Store]