When it comes to software for architectural, interiors, and real estate photography, there are a few items that I'd consider essential. These being a photo editing program, such as Photoshop, and a library and cataloging program such as Aperture or Lightroom. To work without these programs is asking for a miserable time, so hopefully you can use my experience to guide you to whatever software you think is best. I've been an Aperture user for years, but as of October 2013 it seems that Lightroom is slightly better in terms of raw processing and image quality. Aperture's organization flow and layout are far better than Lightroom's, however.
Adobe Photoshop Simply a must have. The creative options that it affords are still second to none. Layers, brushes, adjustments, color corrections, compositing. While you can probably get by without Photoshop, you will probably find yourself aggravated at points and unable to do any sort of compositing. The caveat here is that it can be a real burden to learn. If you have no Photoshop experience, I would start out with just Aperture or Lightroom, which I mention below.
Apple Aperture Aperture is my favorite library and cataloging system, but unfortunately it lags behind Lightroom in terms of raw processing features. Aperture's interface is much more user friendly and a lot faster to use. I've used Aperture for years, and still prefer it to be honest, but since I'm looking to eke the tiniest extra bit of quality out of my images I've been using Lightroom lately. If you're editing a ton of images or shooting frequently, I'd recommend Aperture, but if you're okay with taking slightly longer to do the same thing and a bit clunkier interface for marginally better results, I'd recommend Lightroom. I would love for Aperture 4 to be released soon with features to compete against LR5, but time will tell. Aperture is available as a downloadable app through Apple's App Store.
Adobe Lightroom Lightroom features an amazing array of adjustments and a powerful raw processor. While we filmed the DVD with me using Aperture, in recent months I've switched to Lightroom because I'm okay with sacrificing speed for image quality. The new 'upright' feature is amazing, as well. However, compared to Aperture, the interface is poorly designed, making it take far too long to navigate. You can't customize keyboard shortcuts either, which drives me insane.
