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See the description of RewriteMap in mod_rewrite [httpd.apache.org]. It can call the system "tolower" function to force lowercase. RewriteMap is available in server context, and is not available in per directory (.htaccess) context. Then there is mod_speling [httpd.apache.org] which can correct a few errors in the URL, but at the cost of much slower server performance.
An alternative is to create a custom error document using php or similar, and use it to figure out what URL most closely matches the one that was typed-in. You can use mod_rewrite to check for "file exists" and steer all non-existent requests to this script. If it can fix the URL, fine, then return a 301 redirect to the corrected URL. If not, return a 404-Not Found. Doing this correctly will keep you out of trouble with the search engines.
As far as removing a trailing slash, that's a simple rewrite, and I recommend the documentation cited in our forum charter [webmasterworld.com] to you.
Other than that, take a hard look at your site navigation and try to make it more user-friendly, so that you get fewer type-ins, and pages are easier to find if you issue a 404 and then meta-refresh them to your home page to start over.