Spotify is the perfect example of that...I am forced to use version 0.6 but i can still do almost everything i can with the newest one
Final Cut Pro 6 was tough to find and it did not work with my system when i installed it...I ended up having to use apple's software update tool to update the app and after that it worked amazingly. Unfortunatly this software isnt free so if you want it for free you are going to have to download a pirated copy
Photoshop CS2 and other adobe apps can be found for free if you search CS2 on the adobe website....You can find serials and installers there, everything for free! You do however need to create an Adobe ID to look at them.
An amazing place to find a lot of old Mac software is macintoshgarden.org, its a site where everything can be downloaded for free. There you can find software like iWork/iLife 05 and really old versions of Photoshop. You can also find software on ppcarchive.dyniform.net , that site is really similar to what i am trying to do right here (and even better!).
Torrents
Torrents are a key part of our daily lives and features like magnet support are critical when it comes to torrent clients... For people using 10.5 Leopard your best option is an older version of BitTorrent. It works perfectly and supports magnets with no issues. Mac OSX Tiger is a whole diffetent story, torrent clients that support magnets are almost non-existant. However! Vuze 4.4 works perfectly and supports magnet links ( although you do have to add them mannualy).
Video Playback
CorePlayer is your best bet when it comes to video playback on any PowerPC system. On my iBook G4 720p video plays with no issues, so does 1080p but it is more laggy and choppy. I have tested VLC aswell but i found it sucks and that QuickTime 7 performance is much better. Honestly i would not move from core player as its godly codec manages to make every video playable on the PowerPC architecture. You can find a download link for CorePlayer on macintoshgarden.org