Apple is reportedly working on a new feature for Mac OS X Lion that would rival services like Instapaper and Readability, MacRumors is reporting. Called "Reading List," it's a bookmarking service would allow you to flag and save pages to read later.

"Reading List lets you collect webpages and links for you to read later," reads the description.

MacRumors says the bookmark syncing feature is inactive and is currently hidden in the most recent Lion builds. Reading List isn't mentioned in any of the documentation for the updated OS either.

Apple released a developer preview of Lion about a month ago. It is expected to be unveiled at Apple's annual Worldwide Developers Conference (WWDC) which kicks off on June 6 and will have a focus on software. However, it's likely the full, public version of Lion won't come out until later in the year.

PCMag's lead software analyst Michael Muchmore got an early glimpse of Lion in Febraury. Among some of the never-before seen features he got a look at are AirDrop, a wireless file-sharing utility; a redesigned Mail app; Resume, which presents the OS and Apps in the exact state at shutdown; Versions, which allows app developers to implement a feature that saves multiple snapshots of any documents being worked on; and AutoSave, which does exactly what the name suggests by saving documents automatically.

If Reading List is a part of Lion, it will be a direct challenge to other bookmarking apps like Instapaper, ReadItLater, News.me, and others. However, more Lion features will become apparent over time. Stay with PCmag for more details on Mac OS X Lion as they're revealed.