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Most of the currently popular snippet storage tools are all web-based, meaning you can access them anywhere. The intended goal is to share them with the PHP developer community, but naturally you don't have to share if you don't want to.
Probably the most feature-packed is Gist, the snippet saver offered by the ever-popular Github. All the snippets posted are automatically treated as repositories, meaning they offer all the same benefits as a full Git codebase. They can easily be saved as private or public, although if you create too many it may become difficult to sort through them all.
Next is our personal favourite, Snipplr. It offers much of the same functionality as Gist, but with a handy tagging system that lets you sort quickly through your snippets. It also lets you easily filter based on language, which can be a great help if you're coding in PHP, CSS, HTML5 and JavaScript all at once.
Finally, for a slightly more well-designed version of Snipplr, you can try Snipt, which lets you go from reading this sending to storing your snippets in about 3 seconds. Tagging, descriptions, and private entries available, and if you get mad at the ads, you can opt to go for a Pro account to save your eyes the hassle.
One last entry that deserves a special mention is FastFox, which you can think of as a time-saver for inserting regularly used expressions. It lets you define text-based shortcuts which are automatically converted into larger pieces of text. If you find yourself using a piece of code repeatedly, you can quickly set up a shortcut for it and save yourself a huge amount of time. While it's available for PC and Mac, it's unfortunately not open source, so you'll be shelling out $20 for it - but a free trial is available from their website to help you make up your mind.