Hallo,
simply said:
avastcmd is a standalone application, that attaches the shared VPS blocks, bud does scan on its own. Suitable when you need to scan big directory that contains lots of files (there will be no communication overhead). Doesn't require license. Good for crontab-driven tasks etc.
avastlite is a client for avastd, and thus, suitable for repetitive scans of small files (there will no full-binary-with-full-vps-attach overhead). Good for on-access scanning (when mail/file arrives).
regards,
PC