Some answers to your questions:
Since most of the people are quite busy, I would like to allocate resources to tasks on a specific day. If I want to allocate resources on a daily basis, how do I deal with weekends and National holidays of different countries?
You need to create a list with holidays which you can use to exclude them from your planning. This list can be made configurable for your end-users (strongly recommended for flexibility!). However, it would be nice to add some default holidays. This article explains the logic of some U.S. holidays with Java examples. It would be nice to create a microflow calculating all holidays and upload it to the App Store ;)
Furthermore, in one of your links they refer to a Gantt chart. That's exactly what I had in mind before asking this question. How do I get a Gantt chart look and feel or something like that?
For this you need to create a custom widget. A start can be to use a free FusionChart Gantt Chart, which can be turned into a Mendix widget in an easy way. However, this will involve some JavaScript programming. You can also wait for the release of our App Store and request a Gantt Chart widget from our community.
I think the best is to read some resources on project management and resource allocation. The difficulty in your question is not how to use Mendix but more how you want your resource allocation algorithm to work. If you have the functionality clear, modeling it with the Mendix Business Modeler is quite easy and fast.
See this article for a basic setup of your project. More information with pointers to detailed information can be found here.
What you really need is a good functional idea about what your application should look like. What workflows does it contain? How do your users want to perform these workflows? Etc.
Addon: how exactly do your users want to allocate resources to tasks? Do they first select the dependencies and deadlines for the task? If so, you can provide them with a list of human resources available to perform the task. Or do they also want to select certain users or user groups who need to perform the task?
Thanks for your answer Johan! Very useful links! However, still got some question marks...
Since most of the people are quite busy, I would like to allocate resources to tasks on a specific day. If I want to allocate resources on a daily basis, how do I deal with weekends and National holidays of different countries?
Furthermore, in one of your links they refer to a Gantt chart. That's exactly what I had in mind before asking this question. How do I get a Gantt chart look and feel or something like that?
To generate National holidays per year you can use this tool.
Note: this tool is in Dutch.
The tool Pieter supplied is a nice tool if you want to know what that date is of a holiday in a specific year. But this isn't a generic tool that can be used in your project.
I was involved in a project where we also needed to know all holidays (such as Christmas or eastern) and weekends. A project member I worked with created a microflow which generates an object for all Saturdays and Sundays each day in the weekends and each day that applies as a national holiday at which all companies are legally obligated to be closed.
Unfortunately I can't post the microflow here, but if you want to know how he has build this microflow just contact me.