Most apps are version-specific. An app made for Bada 2.0 (Wave 3) might not run on Bada 1.0 (original Wave S8500) without a firmware update.
Here are popular free apps that were once available legitimately: bada os apps download free
Since official servers are offline, free apps are now hosted by enthusiast communities. Most apps are version-specific
XDA Developers forums, Bada Wave blog, Archive.org collections. Bada Wave blog