1). HCINSTAL.exe - This appears to be the executable that will install the Help Collection.
2).MSSDMN.exe - This is a process related to populating full text indexes. It brings the text data from the SQL Server table to the full-text index.
3). MSSEARCH.exe - Also related to indexing on SQL Server but can also be used for Exchange.
4).OWSTIMER.exe - This is the program that tracks SharePoint's "to do" list. It is critical for alerts and use logs.
5). PRESCAN.exe - This is a program that analyzes your site to identify issues before you upgrade a site.
6). PSCONFIGUI.exe - I think it's the configuration wizard. Still working on it.
7). SPWRITER.exe - This is the volume shadow copy service (VSS) reference writer.
8). STSADM.exe - This is the admin command line console.
9). WSSADMIN.exe - This is the service that runs the various administrative functions.
10). WSSTRACING.exe - Not sure what this one does. It logs records out to the diagnostic log file.
If you've got better links or explanations, I'd love for you to share them.