Rainlendar is a really nice multi-platform calendaring app that I began using back in my Windows days.
The other night I decided to checkout the Rainlendar site to see if by chance there might be a universal package version available. In the past, Rainlendar was only available in a DEB format for the Linux platform and usually required one or more deprecated libraries to run. Much to my delight, I discovered that the developer now offers a static portable build for the Linux platform.
Today I was able to successfully run Rainlendar2 under Solus. I'm using the Openbox window manager and the Tint2 panel as a desktop environment under Solus.
Head on over to the Rainlendar2 site and download the version for Linux 64-bit Other. Once you've downloaded the *.tar.gz file, extract the file to a folder of your choice which will result in the creation of a rainlendar2 folder. I multi-boot Debian Stable, Debian Unstable, and Solus, so I've set up a shared bin folder that I use with all three distros and that's where I extracted the *.tar.gz file. Using a shared bin folder enables me to install one program and use it under all three distros.
The executable path is <path to rainlendar2 folder>/rainlendar2/rainlendar2. You'll have to figure out how to create a menu entry under the Solus flavor that you're using. You should also be able to start Rainlendar2 from the command line using the aforementioned executable path.
Here is my Rainlendar2 setup:
