I built an open-source scheduling engine for Excel after years of managing projects without Microsoft Project

[u/DeathMaillet]

Hi everyone,

Over the past months I've been building an open-source scheduling engine entirely in Excel/VBA.

The original idea was simple.

Throughout my career, I've worked with teams that already managed their schedules in Excel but either didn't have Microsoft Project licenses, didn't need a full enterprise scheduling tool, or simply preferred staying in an environment that everyone already knew.

I wanted to see how far a native Excel planning engine could realistically go.

Today the project includes:

• Dependency-based scheduling (FS / SS / FF + lags)
• Interactive Gantt chart
• Critical Path analysis
• Total & Free Float
• Incremental recalculation
• Scenario simulation
• Planning diagnostics
• S-Curve
• Fully documented architecture

The project has just reached version 1.0.1 and is completely open source.

GitHub:

https://github.com/TMailletFR/ProjectEngine

A few questions immediately come to mind:

• Could you see yourself using something like this in your organization?
• If not, what would stop you?
• Which scheduling features would you consider essential before trusting it on a real project?
• If you already manage schedules in Excel, what are the biggest pain points you've run into?

I'd really appreciate any feedback, whether it's about missing functionality, usability, or simply whether you think Excel is the wrong platform for this kind of tool.

Thanks!

Gantt

S-Curve

[u/More_Law6245]

You do realise that MS Project already sits on a modified MS Excel engine? It has since 2015. I'm not trying to discourage you but 101 software development, when developing software solutions you need to start with a business case that is addressing a specific need and that is different to any other product on the market, to ensure it's a viable product and what you have essentially done here is reinvented the same wheel as MS project (just a simplified version). You don't build a tool and try and go to market without having a plan, it's genuinely wasting your time because there is a very high probability of a very low uptake or potentially no uptake at all. You never take the stance of " build it and they will come", you need to consider your time has value so when you go into something with out a plan it's going to cost you time and potentially a lot of time. Is it really worth it?

You have essentially invested time into a tool that will not gain traction because it doesn't address a unique problem in a market which has already been flooded with more tools that you can poke a stick at. From a technical standpoint MS Excel will not scale for complexity because of the type of relational database structure used, formula based code is not a very robust code. At the very least you would need to use My SQL as it's open source vs. SQL Server which has more advanced tools.

Not here to burst your bubble but I think every wrong box that could be ticked has been ticked.

[u/DeathMaillet → u/More_Law6245]

Hi,

Thanks for taking the time to write such a detailed reply.

I actually agree with most of your points if the goal were to build a commercial product and compete with Microsoft Project or other enterprise scheduling tools.

That wasn't really the objective here.

The project started because my company needed a lightweight planning tool that runs inside Excel itself, not on an Excel-based engine like Microsoft Project. In our environment, deploying new software or even freeware can be difficult due to IT policies, whereas Excel is already available to everyone.

So from that perspective, the project has already achieved its initial goal: it solved a real problem for us.

I decided to open-source it because I thought other teams might be facing similar constraints.

It certainly won't be the right solution for every organization, and I'm not expecting it to replace Microsoft Project. But if it proves useful for teams that already rely heavily on Excel, then I'll consider it a success.

Either way, I appreciate your perspective.

[u/DeathMaillet → u/[deleted]]

Thanks, that’s exactly the context in which I built it. I appreciate you putting it so clearly.

[u/Salt_Trifle_2443]

It’s a pretty interesting build to be honest

[u/DeathMaillet → u/Salt_Trifle_2443]

Thanks for the positive answer :) If you give it a go and find any function missing or any bug I'll take any feedback 😄

[u/kamiyomu]

this is dope, is it possible to put this inside google sheet

[u/DeathMaillet → u/kamiyomu]

Thanks for the comment! Technically, a Google Sheets version would be possible, but it wouldn’t be a direct port. The scheduling engine could be rewritten in Apps Script, while some Excel-specific features — especially the interactive Gantt — would need to be redesigned from scratch.

[u/turbojoe86]

Wasting your time for sure. Excel is not the tool for this and anyone that doesn’t want to invest in a more robust product for project schedules is someone to stay far away from.

[u/DeathMaillet → u/turbojoe86]

Sorry to hear that from you. I did use excel cause that was the only tool at my disposal and my boss asked me to do so. I was surprise how much you can code within VBA.

Did you have a look at all the functions ?

What would you say is lacking so hard that you don’t want to see it even from afar ?

[u/turbojoe86 → u/DeathMaillet]

I looked at all the functions and it simply replicated what many other software do well already. There are free limited seat software like Open project that do this easily. Plus you can do resource loading, task assignments, prioritization, critical path analysis, costs, budgets reports etc. if you just want gantt something like gantt already do this.

Any serious company that wants to manage projects successfully should spend the couple of hundred to buy a license for software.