Service provider seeks multi-client capable cost accounting system

I work as an external service provider and offer cost accounting as a service. I am looking for suitable cost accounting software for this purpose. Preferably, the software should be industry-neutral, but if this is not possible, then it should be suitable for small to medium-sized industrial manufacturing companies.

The software should support the following processes:

• Full cost and partial cost accounting
• Actual and planned cost accounting
• Marginal cost accounting
• Contribution margin accounting
• Possibly step-by-step fixed cost accounting

Further requirements are:

• Multi-client capability (mandatory criterion)
• Standalone solution (mandatory criterion)
• Initially runnable on a single workstation with the option of migrating to a server at a later date
• Import of master data and accounting data from Excel files, if available in a suitable format
• Industry-neutral (see above)

Initially, one software workstation is planned. If necessary, the system will be expanded to 2-3 systems at a later date.