Where they can be downloaded from I can't tell you, but here a short description of the names that are used for clients and servers:
- Domino is the server
- the Notes client is the standard user client
- iNotes is nothing more than an extension to the server (Internet Notes) that enables you to use a browser for mail access
- the Domino Administrator client is the client for administrative purposes (admin tools)
- the Domino Designer client is used for developing and maintaining applications
The Domino server is available on many O/S environments: Windows, Linux, Unix, etc. There are Notes clients on Windows and Macintosh, and since R8 also on Linux. The Designer client runs on Windows, and the Admin client I'm not sure of.
Hope this helps you a little.