Adobe has announced the beta release of Adobe Digital Editions, a Windows-based, freeware PDF/eBook reader and library manager. From the FAQ:
Digital Editions is a focused, lightweight solution (2.5MB download). It extends the eBook capabilities that were integrated in previous versions of Reader and Acrobat, delivering a simplified, content-centric consumer-friendly user interface. Digital Editions is distributed as a web-based RIA, ensuring that users will always have the current up-to-date version of the software.