Loansome Doc is the document ordering component of PubMed, the free, public version of MEDLINE developed by the National Library of Medicine and the National Center for Biotechnology Information. This service enables you to request documents by simply checking off the articles you want from your search results, selecting "Order" from the "Send to:" menu, and typing in a password. Your request then goes directly to the medical library where you have established an account.
For more information about Loansome Doc, see the fact sheet  on the NLM website.
Yes, the Lewis Library system for Document Delivery/Interlibrary Loan provides features and benefits that are very similar to Loansome Doc. An account in that system is required for online delivery of copies, so you may want to use it consistently for all your requests. However, only one request at a time can be sent to the Lewis Library system, so an additional Loansome Doc account can be helpful if you typically order multiple documents at once from PubMed. It also provides a more efficient workflow for those who are not affiliated with the UNT Health Science Center.