[rwhitman]

Patents are probably the most powerful tool for entrenched players here. Adobe patented several GUI conventions including their most common shortcut key commands in Photoshop, so that competitors would always have a slight learning curve for new users.

Occasionally more aggressive companies will come after a cloned product with a lawsuit, for instance Facebook sued a number of early competitors for various intellectual property and trademark reasons. Doesn't hold up in court publicly but I imagine there have been a lot of backroom settlements made this way over the years.