Download of myOSM 1.3 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. MyOSM for Mac lies within System Tools, more precisely Device Assistants. We recommend checking the downloaded files with any free antivirus. The actual developer of this free Mac application is Dirk Stichling.
From the developer:
myOSM is an online and offline viewer for various map types such as OpenStreetMap, Cloudmade, and OpenCycleMap. myOSM can also show your current location on the map. There are some major advantages over the corresponding webpages: The maps can be accessed if not being connected to the internet. The various map types can be accessed within the same GUI. Bookmarks for easy access of often used locations. Nearly fullscreen view of the maps.
You may want to check out more software for Mac, such as Line 6 Monkey, i-Installer or TunesArt, which might be related to myOSM.