There are a lot of E-signature companies offering this service, but for signing IRS 8878/8879, it has to have KBA (Knowledge Based Authorization), such as Docusign uses. Others that meet this requirement are CCH E-sign, Smartvault and I think Adobe. If there are others, I haven't run across them. KBA requires two questions to be answered electronically, usually DOB and SSN accessed through a credit agency.
If I am reading the following correctly, the IRS will accept faxed, or emailed wet signatures.
"What is an “e-signature via remote transaction” in relation to Forms 8878 or 8879?
A remote transaction for e-signature is one in which the taxpayer is electronically signing the form and the ERO is not physically present with the taxpayer.
Note: A remote transaction for e-signature purposes does not include handwritten signatures on Forms 8878 or 8879, sent to an ERO by hand delivery, U.S. mail, private delivery service, fax, e-mail or an Internet website."
https://www.irs.gov/e-file-providers/frequently-asked-questions-for-irs-efile-signature-authorization