I have been looking at various options to move from Actinic V10 to a web-based store admin.
Big Commerce looked attractive but on further investigation it is really limited for B2B and inflexible in terms of additionial product information tabs, extra side info panels, etc.
Many other SaaS options seems to be only retail or have similar restrictions in template functionality.
Any suggestions for SaaS or self-hosted software to give customised functionality similar to Actinic?
You could take a look at Pinnacle Cart (just building a new store with Pinnacle Cart as we speak, going very well so far)...it seems to do the majority of basic functionality and then some.