The developers of SimpleNote have made their API available for free, and a number of Mac and PC applications are now available to eliminate the need to log into the SimpleNote website. I tried several of the Mac programs to see how they worked. The first, JustNotes from SelfCoded, shows a lot of promise. It brings up a small transparent window with note area upon clicking a menu bar icon, then displays the notes that are currently in your SimpleNote account. It's still in beta, and I ran into some issues when deleting notes from the iPhone app -- they wouldn't automatically disappear from the Mac as they should have.
Developer Alex Payne has created a website for backup and export of SimpleNote data. His free website exports your notes into plain text, CSV, JSON, XML, YAML, and Evernote archive formats. Fletcher Penney has developed a Perl script for synchronizing a folder of text files with SimpleNote. As with many of these "aftermarket apps,", SimplenoteSync is free, but a donation is suggested if you use the software.
SNYS (SimpleNote Yojimbo Sync) is another handy script for syncing notes between Yojimbo (US$39, from Bare Bones Software) and SimpleNote on the iPhone. While I have not had a chance to try out SNYS, it could be a great interim solution for Mac fans who are stymied by the lack of a iPhone version of Yojimbo.
If you're a user of the Habari blogging platform, there's a plugin to allow you to use SimpleNote as an iPhone blogging tool.
In comparison to the other note apps that are available for iPhone, I'd say that WriteRoom for iPhone [US$4.99, iTunes Link] probably comes the closest to SimpleNote in terms of usability and functionality. It syncs with WriteRoom.ws, and like SimpleNote it provides the ability to write and edit notes in landscape mode. Both apps also provide support for TypeExpander Touch [US$4.99, iTunes Link], allowing you to create abbreviations for long snippets of text. WriteRoom for iPhone does provide full-screen editing, something that isn't available with SimpleNote.
All other things being somewhat equal, I would still choose SimpleNote over WriteRoom because of the price -- it's $3 cheaper -- and the fact that it just works simply and quickly. If it's just Wi-Fi syncing that you're looking at, I'd suggest looking at Tapbots' new PasteBot app [US$1.99, iTunes Link] or Erica Sadun's PasteCatcher, a bargain at just US$0.99 [iTunes Link].
For those of you who want to be able to do syncing of notes "in the cloud" from any place you have a data connection, SimpleNote is a bargain and a great addition to your iPhone. Be sure to check out the gallery below for some screenshots from SimpleNote and the JustNotes Mac application.